AS needs to have the aircraft in with wheels blocked by 6:25 PM to use the clearance facilities at T-6. If not it's TBIT and probably a remote gate experience with a bus ride. When I re-entered the country earlier this month, it was about 30 minutes until I was at the baggage claim (GE) and took another 10-15 minutes for bags to start to appear. Then clear customs, and walk to T-6 not to mention security. So 90 minutes might be ok without bags if everything goes well. If not, or add luggage, it might get a bit messy.