add hours, days, weeks, months to any date in magento

      $date = date("Y-m-d");

      $mydate = strtotime(date("Y-m-d", strtotime($date)) . " +3hours");

      $mydate = strtotime(date("Y-m-d", strtotime($date)) . " +1 day");

      $mydate = strtotime(date("Y-m-d", strtotime($date)) . " +1 week");

      $mydate = strtotime(date("Y-m-d", strtotime($date)) . " +30 days");

      $mydate = strtotime(date("Y-m-d", strtotime($date)) . " +1 month");