00-direct-database-query.php

<?php

// First, update the post using the available WordPress API.
wp_update_post( $post );

/**
 * If the post status attribute of the post that was just updated
 * maintains the 'publish' post setatus, then manually update the 
 * database column.
 */
if ( 'publish' === $post->post_status ) {

	global $wpdb;
	$wpdb->query(
		$wpdb->prepare(
			"
			UPDATE $wpdb->posts
			SET post_status = '%s'
			WHERE ID = %d
			",
			'publish',
			$post->ID
		)
	);
}

01-maintain-post-status.php

<?php

$event_post->post_date_gmt = gmdate( 'Y-m-d H:i:s', $event_post->post_date_gmt );
wp_update_post( $event_post );

02-update-post-conditional.php

<?php

if ( 'attachment' !== $post_type ) {
	if ( 'publish' == $post_status ) {
		$now = gmdate('Y-m-d H:i:59');
		if ( mysql2date('U', $post_date_gmt, false) > mysql2date('U', $now, false) ) {
			$post_status = 'future';
		}
	} elseif ( 'future' == $post_status ) {
		$now = gmdate('Y-m-d H:i:59');
		if ( mysql2date('U', $post_date_gmt, false) <= mysql2date('U', $now, false) ) {
			$post_status = 'publish';
		}
	}
}

03-apply-filters-post-status.php

<?php

$post_parent = apply_filters( 'wp_insert_post_parent', $post_parent, $post_ID, compact( array_keys( $postarr ) ), $postarr );

04-post-date-gmt.php

<?php

if ( empty( $postarr['post_date_gmt'] ) || '0000-00-00 00:00:00' == $postarr['post_date_gmt'] ) {
		if ( ! in_array( $post_status, array( 'draft', 'pending', 'auto-draft' ) ) ) {
			$post_date_gmt = get_gmt_from_date( $post_date );
		} else {
			$post_date_gmt = '0000-00-00 00:00:00';
		}
	} else {
		$post_date_gmt = $postarr['post_date_gmt'];
	}