Source

File: wp-includes/general-template.php

function get_post_datetime( $post = null, $field = 'date', $source = 'local' ) {
	$post = get_post( $post );

	if ( ! $post ) {
		return false;
	}

	$wp_timezone = wp_timezone();

	if ( 'gmt' === $source ) {
		$time     = ( 'modified' === $field ) ? $post->post_modified_gmt : $post->post_date_gmt;
		$timezone = new DateTimeZone( 'UTC' );
	} else {
		$time     = ( 'modified' === $field ) ? $post->post_modified : $post->post_date;
		$timezone = $wp_timezone;
	}

	if ( empty( $time ) || '0000-00-00 00:00:00' === $time ) {
		return false;
	}

	$datetime = date_create_immutable_from_format( 'Y-m-d H:i:s', $time, $timezone );

	if ( false === $datetime ) {
		return false;
	}

	return $datetime->setTimezone( $wp_timezone );
}