How long in minutes is it from returning your car to arriving at the airport check in via air train?

Less than 10 mins

10 minutes.

Timed it recently, until terminal C it's around 20 minutes!

I'm here now. Matters how busy. 10 to 15 minute. Avis has a service that will drop at your terminal. Save a lot of time. They return the car for you. Cost $20.00

Agree with the other answer, about 10 minutes.