I have almost the same setup. The door from our Garage to Mudroom never seems to gets closed all the way and a breeze with push it open causing Heat or AC to escape not to mention let bugs in during the spring/summer/fall months. I found a SmartApp called Super Notifier that does what your looking for. I have mine setup to push alert all phones in the household when open 3 Minutes and then every 1 minute after that until closed then it will send a “Now Closed” alert as well.
You can find Super Notifier here… [RELEASE] Super Notifier - All your alerts in one place!