When I did this last August, the wait was 3 hours on I5. So I diverted at a little border park and went back to the "truck crossing." The wait at the truck crossing, which takes cars too, was short -- but the traffic was a mess on the eastbound exit from I5 because trucks couldn't turn onto the road for the crossing due to the truck queue. This backed up cars as well. It appeared there was an approach from the north which was much faster, so you should leave the freeway a few exits north of the border to get to it -- have a good map!

Sad that it's come to this.