Delays at the Blaine, WA border are mostly when Canadians travel to buy things. During the weekends, Canadians might drive on Saturday morning and come back Sunday evening. Southbound border waits are longer on Saturday morning and northbound waits are longer on Sunday evening.

The opposite direction, what Americans would do, isn't very long. Sometimes southbound on Sunday evening is a bit of a wait but always shorter than the opposite. That's because more Canadians come to look and shop while Americans know that Canadian things are expensive so only lookers come, not shoppers.