How to set publishing date and time for a WordPress post Programmatically?

The short answer for the “How to set date and time for a WordPress post programmatically” question is here:

$id = 1;
$date_time = "2021-12-31 23:59:59";//[Y-m-d H:i:s]
wp_update_post(
    array (
        'ID' => $id,
        'post_date' => $date_time,
        'post_date_gmt' => get_gmt_from_date( $date_time )
    )
);

The above codes will update a post with the id number 1 and set the post publishing date.

Here is more explanation if you are interested:

wp_update_post() function can update a post in WordPress, using an array of attributes with value.

You must pass the id of the post you wish to update, using the ID attribute.

You can set post_date and post_date_gmt to change the post publishing date to whatever you want.

Proper structure for post_date attribute is Y-m-d H:i:s

If you want to know how to query posts in WordPress using publish date, you can read my tutorial:

WordPress Query Posts by Category, Tag, Custom attribute, and more!