It's a good thing you restated YUL in this response, since I couldn't figure out why CBP closed at 8, instead of 9 as I know they do in YYZ. I didn't pay attention to the route of the original LAS flight with the delay and said YYZ because later in the delay message there was an AOG aircraft in YYZ. Dumb dumb dumb me.

Anyhow so YYZ CBP closes at 9, and YUL at 8.

Did they post the delay accurately after 8pm? I know in YYZ they do (post the delay once CBP closes)