Add a PIR on a input and have it read that input. If the input lets say goes high, have it reset your 5 minute timer back to start. That way if your in your garage or someone else is it will constantly reset it. I have the same exact thing made in my garage and it works great. The only difference is I used a dip switch and read it to determine the time frame to leave the door open. This way I can set it from 5 minutes to 1.5 hours.
Don't forget to add denounce to your disable switch. Otherwise it will false. I have code for that if you want it.
One last thing. Have the PIR hooked to a interrupt line. Have the interrupt reset the time via code.