How to change post date only 1 time a day?

Question

I have this code

is_admin() or add_action( 'the_post', function( $post ) {

if ( ! is_singular() or ! is_main_query() )
    return;

$post->post_date     = current_time( 'mysql' );
$post->post_date_gmt = '';

wp_update_post( $post );

});

When refreshing the page, it will update to current time. But this will slow down my site. So how to update date time of page to current time only 1 time per day ?

Example: I write a post on 5pm, June 6, 2013. And now, when I refresh page, it will change from 5pm, June 6 to 7pm, June 9. And in June 9, if I refresh the page, it will not change anything.

Sorry for my poor English ! Thank you very much !

Answer 1

Compare the post_date with the current time and then test if the difference is greater than one day:

is_admin() or add_action( 'the_post', function( $post ) {

    if ( ! is_singular() or ! is_main_query() )
        return;

    // now minus last mod time in seconds
    $diff = time() - mysql2date( 'U', $post->post_date );

    if ( DAY_IN_SECONDS >= $diff )
        return;

    $post->post_date     = current_time( 'mysql' );
    $post->post_date_gmt = '';

    wp_update_post( $post );
});