magento2: Cannot create full datetime product attribute

@jzahedieh yea sorry for the wait. It’s been a while, but I think these are all the pieces. Keep in mind this code is from like a year ago, I think we were still on 2.0.* or something. So for the helper preference, you might want to check on that copy-pasted stuff and make sure it’s up to date.

New datetime form element

Block/Adminhtml/Form/Element/Datetime.php

<?php
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
namespace BlueAcorn\ContentPublisher\Block\Adminhtml\Form\Element;

use Magento\Framework\Data\Form\Element\Date;

/**
 * Class Datetime
 *
 * Created to allow full date+time picker on eav attribute. See \Magento\Backend\Block\Widget\Form methods
 * _setFieldset and _applyTypeSpecificConfig for why this is necessary.
 */
class Datetime extends Date
{
    /**
     * Override to force date and time formats before rendering html
     *
     * @return string
     * @throws \Exception
     */
    public function getElementHtml()
    {
        $this->setDateFormat($this->localeDate->getDateFormat(\IntlDateFormatter::SHORT));
        $this->setTimeFormat($this->localeDate->getTimeFormat(\IntlDateFormatter::SHORT));
        return parent::getElementHtml();
    }
}

Use it in install script

Setup/InstallData.php

<?php
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
namespace BlueAcorn\ContentPublisher\Setup;

use Magento\Eav\Setup\EavSetup;
use Magento\Eav\Setup\EavSetupFactory;
use Magento\Framework\Setup\InstallDataInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\ModuleDataSetupInterface;

class InstallData implements InstallDataInterface
{
    /**
     * EAV setup factory
     *
     * @var EavSetupFactory
     */
    private $eavSetupFactory;

    /**
     * Init
     *
     * @param EavSetupFactory $eavSetupFactory
     */
    public function __construct(EavSetupFactory $eavSetupFactory)
    {
        $this->eavSetupFactory = $eavSetupFactory;
    }

    /**
     * {@inheritdoc}
     */
    public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
    {
        /** @var EavSetup $eavSetup */
        $eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
        $eavSetup->removeAttribute(\Magento\Catalog\Model\Product::ENTITY, 'publish_start');
        $eavSetup->addAttribute(
            \Magento\Catalog\Model\Product::ENTITY,
            'publish_start',
            [
                'label' => 'Enable Start Date',
                'type' => 'datetime',
                'input' => 'date',
                'input_renderer' => 'BlueAcorn\ContentPublisher\Block\Adminhtml\Form\Element\Datetime',
                'class' => 'validate-date validate-date-range date-range-publish-from',
                'backend' => 'BlueAcorn\ContentPublisher\Model\Entity\Attribute\Backend\Startdate',
                'required' => false,
                'group' => 'Product Details',
                'sort_order' => 18
            ]
        );
        $eavSetup->removeAttribute(\Magento\Catalog\Model\Product::ENTITY, 'publish_end');
        $eavSetup->addAttribute(
            \Magento\Catalog\Model\Product::ENTITY,
            'publish_end',
            [
                'label' => 'Enable End Date',
                'type' => 'datetime',
                'input' => 'date',
                'input_renderer' => 'BlueAcorn\ContentPublisher\Block\Adminhtml\Form\Element\Datetime',
                'class' => 'validate-date validate-date-range date-range-publish-to',
                'backend' => 'Magento\Eav\Model\Entity\Attribute\Backend\Datetime',
                'required' => false,
                'group' => 'Product Details',
                'sort_order' => 19,
                'note' => __('If you want to keep a product enabled indefinitely, leave the start and end dates empty.'
                    . ' If an "Enable End Date" exists, the product will remain disabled after the end date has passed.')
            ]
        );
    }
}

Overwrite product initialization helper

etc/di.xml

<?xml version="1.0"?>
<!--
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Catalog\Controller\Adminhtml\Product\Initialization\Helper"
                type="BlueAcorn\ContentPublisher\Helper\Adminhtml\Catalog\Product\Initialization" />
</config>

Helper/Adminhtml/Catalog/Product/Initialization.php

<?php
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
namespace BlueAcorn\ContentPublisher\Helper\Adminhtml\Catalog\Product;

use Magento\Catalog\Controller\Adminhtml\Product\Initialization\Helper as CatalogHelper;

/**
 * Class Initialization
 * Rewriting class to allow date+time on datetime attributes
 */
class Initialization extends CatalogHelper
{
    /**
     * @var \Magento\Framework\Stdlib\DateTime\Filter\DateTime
     */
    protected $dateTimeFilter;

    /**
     * @param \Magento\Framework\App\RequestInterface $request
     * @param \Magento\Store\Model\StoreManagerInterface $storeManager
     * @param \Magento\Catalog\Controller\Adminhtml\Product\Initialization\StockDataFilter $stockFilter
     * @param \Magento\Catalog\Model\Product\Initialization\Helper\ProductLinks $productLinks
     * @param \Magento\Backend\Helper\Js $jsHelper
     * @param \Magento\Framework\Stdlib\DateTime\Filter\Date $dateFilter
     * @param \Magento\Framework\Stdlib\DateTime\Filter\DateTime $dateTimeFilter
     */
    public function __construct(
        \Magento\Framework\App\RequestInterface $request,
        \Magento\Store\Model\StoreManagerInterface $storeManager,
        \Magento\Catalog\Controller\Adminhtml\Product\Initialization\StockDataFilter $stockFilter,
        \Magento\Catalog\Model\Product\Initialization\Helper\ProductLinks $productLinks,
        \Magento\Backend\Helper\Js $jsHelper,
        \Magento\Framework\Stdlib\DateTime\Filter\Date $dateFilter,
        \Magento\Framework\Stdlib\DateTime\Filter\DateTime $dateTimeFilter
    ) {
        $this->dateTimeFilter = $dateTimeFilter;
        parent::__construct(
            $request,
            $storeManager,
            $stockFilter,
            $productLinks,
            $jsHelper,
            $dateFilter
        );
    }

    /**
     * Initialize product before saving
     *
     * @param \Magento\Catalog\Model\Product $product
     * @return \Magento\Catalog\Model\Product
     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
     * @SuppressWarnings(PHPMD.NPathComplexity)
     */
    public function initialize(\Magento\Catalog\Model\Product $product)
    {
        $productData = $this->request->getPost('product');
        unset($productData['custom_attributes']);
        unset($productData['extension_attributes']);

        if ($productData) {
            $stockData = isset($productData['stock_data']) ? $productData['stock_data'] : [];
            $productData['stock_data'] = $this->stockFilter->filter($stockData);
        }

        foreach (['category_ids', 'website_ids'] as $field) {
            if (!isset($productData[$field])) {
                $productData[$field] = [];
            }
        }

        $wasLockedMedia = false;
        if ($product->isLockedAttribute('media')) {
            $product->unlockAttribute('media');
            $wasLockedMedia = true;
        }

        $dateFieldFilters = [];
        $attributes = $product->getAttributes();
        foreach ($attributes as $attrKey => $attribute) {
            if ($attribute->getBackend()->getType() == 'datetime') {
                if (array_key_exists($attrKey, $productData) && $productData[$attrKey] != '') {
                    // BEGIN BA CHANGES
                    $dateFieldFilters[$attrKey] =
                        ($attribute->getFrontendInputRenderer() == 'BlueAcorn\ContentPublisher\Block\Adminhtml\Form\Element\Datetime')
                            ? $this->dateTimeFilter
                            : $this->dateFilter;
                    // END BA CHANGES
                }
            }
        }

        $inputFilter = new \Zend_Filter_Input($dateFieldFilters, [], $productData);
        $productData = $inputFilter->getUnescaped();

        $product->addData($productData);

        if ($wasLockedMedia) {
            $product->lockAttribute('media');
        }

        if ($this->storeManager->hasSingleStore()) {
            $product->setWebsiteIds([$this->storeManager->getStore(true)->getWebsite()->getId()]);
        }

        /**
         * Check "Use Default Value" checkboxes values
         */
        $useDefaults = $this->request->getPost('use_default');
        if ($useDefaults) {
            foreach ($useDefaults as $attributeCode) {
                $product->setData($attributeCode, false);
            }
        }

        $links = $this->request->getPost('links');
        $links = is_array($links) ? $links : [];
        $linkTypes = ['related', 'upsell', 'crosssell'];
        foreach ($linkTypes as $type) {
            if (isset($links[$type])) {
                $links[$type] = $this->jsHelper->decodeGridSerializedInput($links[$type]);
            }
        }
        $product = $this->productLinks->initializeLinks($product, $links);

        /**
         * Initialize product options
         */
        if (isset($productData['options']) && !$product->getOptionsReadonly()) {
            // mark custom options that should to fall back to default value
            $options = $this->mergeProductOptions(
                $productData['options'],
                $this->request->getPost('options_use_default')
            );
            $product->setProductOptions($options);
        }

        $product->setCanSaveCustomOptions(
            (bool)$this->request->getPost('affect_product_custom_options') && !$product->getOptionsReadonly()
        );

        return $product;
    }
}

If you are implementing start/end, set max value stuff

etc/adminhtml/events.xml

<?xml version="1.0"?>
<!--
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="catalog_product_validate_before">
        <observer name="setStartDateMaxValue" instance="BlueAcorn\ContentPublisher\Observer\Adminhtml\Product\SetStartDateMaxValue"/>
    </event>
</config>

Observer/Adminhtml/Product/SetStartDateMaxValue.php

<?php
/**
 * @package     BlueAcorn\ContentPublisher
 * @version     1.0.0
 * @author      Sam Tay @ Blue Acorn, Inc. <code@blueacorn.com>
 * @copyright   Copyright © 2016 Blue Acorn, Inc.
 */
namespace BlueAcorn\ContentPublisher\Observer\Adminhtml\Product;

use Magento\Framework\Event\Observer as EventObserver;
use Magento\Framework\Event\ObserverInterface;

/**
 * Class SetStartDateMaxValue
 * Observes catalog_product_validate_before
 * Purpose: Set max value on start date equal to end date value
 */
class SetStartDateMaxValue implements ObserverInterface
{
    /**
     * Execute observer
     * @param EventObserver $observer
     */
    public function execute(EventObserver $observer)
    {
        /** @var \Magento\Catalog\Model\Product $product */
        $product = $observer->getEvent()->getProduct();
        $product->getResource()->getAttribute('publish_start')
            ->setMaxValue($product->getPublishEnd());
    }
}

I opened this issue in 2016… haven’t worked on Magento in years. Congrats though!