This is weird (and new).
Checkin and baggage cutoff has always been 60 mins. I m pretty sure last month I got off the bus at 5:25, and made my 6:20 flight to DEN with ease, stopping for coffee at the MLL.
But as others have mentioned, if you do not have Nexus/GE - customs at T1 can take an hour on a good day, and probably more now with the new restrictions