simple storewide sale set a schedule for sale 18:00 to 19:00 daily

add_action( 'init', 'custom_schedule_storewide_sale', 90 );

function custom_schedule_storewide_sale() {

    $start_time = '18:00';
    $end_time   = '19:00';

    $sale_to = get_option( 'wcsss_end', false );

    if ( isset( $sale_to ) && ! empty( $sale_to ) ) {
        $date1 = new DateTime( $sale_to );
        $date2 = new DateTime( current_time( 'mysql' ) );
        if (  $date1 < $date2 ) {
            $new_sale_to = date( "Y-m-d H:i:s", strtotime( "tomorrow ". $end_time ) );
            $new_sale_from = date( "Y-m-d H:i:s", strtotime( "tomorrow " . $start_time ) );
            update_option( 'wcsss_end', $new_sale_to );
            update_option( 'wcsss_start', $new_sale_from );
        }

    }
}