It's an interesting question. Over the years I think I've crossed the border, North or South at every hour at some point. Used to prefer crossing South at night, until the highway banditos of 09' era. But just came across yesterday ( Monday 4th, North ) arrived at the border 10ish, and was backed up. Was about 1/2 way between the last turn and Wendy's Hill. Was the first time in a while that traffic just wasn't moving. I think our wait time was 50+ minutes. I've been in line before and traffic was backed up to the last turn, and was about the same 50 minute wait time. Guess what I'm saying is that it doesn't always matter what time of day or night or the amount of traffic, it's how quickly the border agents are processing people.