Are you charged for the first hour as soon as you enter the garage? Or is there a 15 minute or so grace period in which you can leave without being charged?

Regular days, you have 10 minute grace period. During the holidays, that grace period is 30 minutes. After that you will be charged $6 for the hour

At this time it's 60 mins free in the garage and 20 mins free at Terminal Parking. I went there last Friday.

I thought that you're changed for all of time in the in the garage but the parking lot in front of the terminal has some free time. I'm not sure.