I don't know about last year, but the 4 years we did it, I don't think we ever got back before 3. One year, someone on one of the first busses left his passport in his luggage, in spite of many many reminders to keep it on your person, so they had to take ALL the luggage off the bus at the border crossing, search for the guy's bag, find it, run every body through the line, get the dogs to check the bags, reload etc... I think we were waiting at the border for 3 hours! Another year, we just had an agent board the bus, quickly look around and see that everyone did indeed possess a passport and we were through in 10 minutes. I would plan for the longer time, though. you just don't want to risk missing your flight.