<?php
namespace Olegnax\Athlete2\Block\Adminhtml\System\Config;

use Magento\Config\Block\System\Config\Form\Field;
use Magento\Framework\Data\Form\Element\AbstractElement;
use Magento\Framework\Stdlib\DateTime;

class DatePicker extends Field
{

    public function render(\Magento\Framework\Data\Form\Element\AbstractElement $element)
    {
        $element->setDateFormat(DateTime::DATE_INTERNAL_FORMAT);
        $element->setTimeFormat('HH:mm:ss');
        $element->setShowsTime(true);
        return parent::render($element);
    }
}