I got in and out a few days ago with no charge so there is still some type of grace period. I was only in the garage for 2-3 minutes though. The supercharger was near full so the parking was tight and I simply decided that I didn't need the charge that badly (was only considering it because I was meeting someone 2-3 blocks away).FYI the free 30 minutes is no longer a thing, it is now minimum $7, although they do validate at Dough Zone can I get an amen.
My guess is the grace period is 10 or 15 minutes now which isn't really practical for 72kW supercharging.