\WP_Stager_Integration\Calendar::get_day_number(int $timestamp = null): int

Full Code

/**
 * Get a formatted day number (1-31). Takes the site's timezone setting into account.
 *
 * @param int    $timestamp  (Optional) The Unix timestamp to get the number for. Defaults to current server time.
 *
 * @return int  The day number (1-31)
 */
public static function get_day_number( $timestamp = null ) {

    // Type casting
    $timestamp = (int) ($timestamp ?: time());

    return (int) wp_date( 'j', $timestamp );
}