My 2 cents...This holiday (Semana Santa) is almost entirely made up of Nationals. They will come from Nogales, San Luis, Mexicali and Tijuana none of which pass through the Lukeville crossing. Add to that group Mexicans that live in Phoenix - Tucson - and Southern California that will make the trip to be with families here in Penasco. That number is hard to determine (Mexicans from the states coming here) but it could be significant based on the numbers that have been forced to move to Mexico from Arizona in the last few years. If I had to be in Phoenix at 2:00 pm Sunday I would leave no later than 7:00 - 7:30 Sunday morning, I have a half a notion it could be backed up as early as noon (condos check out at 11:00) it only takes one hour to get to the border but if you get there at the same time as everyone who is checking out it could turn 15 minutes wait into 2-3 hours easily and the border guards on the US side (even though theres a post about friendly ones) have been increasingly time consuming per each car. They will be especially diligent when the traffic going north is increased with Mexican/American travelers going home to Phoenix or Tucson from Mexico.
Having said all that I could be completely wrong and it could be smooth sailing, but if I was a betting man and I had to be somewhere at a certain time north of the line, I would err on the side of prudence. 2 cents o 3 pesos