Geez! I read STD and was pretty sure it meant Stanstead and when I was about to reply, I realized "STN" was Stanstead so I erased everything.
Then looked down, I read the OP meant to put in "STN" not "STD."
Now I am typing it all over again! THANKS ALOT!
Anyways, STN has ridiculously long lines at times. Check-in was about 30 minutes and immigration was another 30 minutes. Yep, I'd place it at 50:50.