Disable notification during certain hours

<?php
// http://www.gravityhelp.com/forums/topic/user-notification-during-specific-hours#post-61964
// change 81 here to the form for which you want to disable notifications
add_filter('gform_disable_user_notification_81', 'disable_user_notification', 10, 3);
function disable_user_notification($is_disabled, $form, $entry){
        // the hour of the day now, 24 hour format
        $hour = date('G');
        // if the hour is 10 or after, AND 21 or before, then disable the notification
        if ($hour >= 10 && $hour <= 21)
                return true;
        else
                return false;
}