/**
  * instance method
  *
  * Singleton creation method, to allow saving resources and having single
  * object instance throughout system.
  *
  * @return Ai1ec_Time_Utility Single instance of self
  */
 public static function instance()
 {
     if (!self::$_instance instanceof Ai1ec_Time_Utility) {
         self::$_instance = new Ai1ec_Time_Utility();
     }
     return self::$_instance;
 }