I believe that’s correct, but then the question becomes what is there to do for 4h airside. As far as I know, there isn’t much to do.

If the OP heads landside there are more options, and either way you have to clear US immigration. Doing it from a domestic flight might reduce security (never done Dom to TB at YYZ) but it’s unlikely OP is going to be short of time.

It’s definitely not open 24/7. But given the daily 6am YYZ ORD flight I gotta hope it opens before 5am, especially when YYZ says to get there 3h before 10am flights. Earliest I’ve done it was around 6 (for an 8am).