As it turns out, no.
I took them out of the cooler, left them in their bags, put them in the fridge, said three "Hail Kenjis" and went to sleep.
Next day at lunch I opened the bags, wiped off grease and coagulated burger juice, salted them and put them on the oiled griddle on the gas BBQ.
Because they were cold I could let them stay a little longer than usual. Result: great crust, correct color, good burgers at a good temperature.
Note that I like my patties at 9 oz and Marty prefers 6 oz but both were just fine.
The only downside is that I thought they were a tad less juicy than usual. Sounds like a job for Burger Lab.
Kenjiburgers are not only better than what I used to make, they're now all but stress-free. You have to work at it to F*&^ them up.