All of the news reports I've seen on the TSA mess at MSP have apparently been about T1: The pictures of lines are from T1, passengers and airline staff shown are from DL, and it's T1 where TSA created the mess by reconfiguring the checkpoints in February. However, you should recognize that early morning has always been the time when lines at MSP are longest, sometimes shockingly so for the approximately 6 am bank of flights even before the recent mess.

My instinct is always to avoid returning a rental car by leaving the keys because the chances of being billed for damage or overtime seem to be too great. However, if you ahve really good primary credit card insurance coverage, you might not care.

To me, returning the car at 6 am at T2 (Will there be a line then just to return the car? I have no idea, but I'd be concerned.) would be far too late for a 6:50 departure, as would thhe 5 am option at T1 given that the light rail will not be frequent then.

I would either pick a 24 hour T1 return rental agency and get there at about 4 am or stay the night at one of the airport hotels with an early (be sure to make a reservation and get to the lobby early as space can be limited at that hour) free shuttle service. Many airport hotels have either on demand shuttles 24/7 or do a first run at 4 am; allow about 25 minutes for the trip.