Hopefully some of the pro's will come on, but since you are going to do this tonight I will say this.
I'm not real sure, but I think Barry said something about more shrinkage over time reducing the sand scratches, and they should be resanded before painting. I don't remember the time line, but what do have to loose?
Won't take any time at all to re-scuff. Theres a thread floating around here somewhere on this. If the primer was fully cured before sanding, and think you are OK. But if it was sanded a day or 2 after spraying, the scratches will shrink back up. This is true for any 2k urethane primer...even those that sell for $300 a kit. So many variables go into play here...including temp..how it was sprayed...etc. Safest bet is to rescuff before sealer. Nothing to lose...but a lot to lose if you don't and something happens. Just my 2 cents!!
Everyone does things a little differently. For instance, I would never sand something 2 weeks before painting it. If it happened accidentally, it really doesn't take much time to go over it real quick to ensure a fresh clean surface to paint on for peace of mind and maximum adhesion. To me it's not worth the chance just to save on a little elbow grease.
A quick dry scuff wouldn't take but 20 minutes just to make sure there isn't adhesion problems but I bet they'll be just fine if the primer was fully cured.
Bondo after 12 hours, no urethane primer is done shrinking.. None of them really., As the weeks go by the primer will shrink and reduce the scratch that you put in it.. The reason they are telling him to scuff is to make sure he has full adhesion.. 20-30 minutes of his time and no worries about adhesion problems down the line is all..
If the primer had set for a week for instance, then sanded.. It could set indefinitely before spraying without issue if my memory serves me correct.. But most will spray today, sand tomorrow.. As long as you paint over that soon...NO PROBLEM.. Done every single day all over the country in collision shops!! However if you let it set for a couple of weeks sanded as he has done.. It can create an adhesion problem... Notice I said Can.. Not WILL!!!
Always better to err on the side of caution!! 20 minutes, vs chipping, peeling issues or a re paint.. You get the point!!
I just spoke with Barry on this a day ago...I sprayed 2k turbo about a month ago and blocked with 400, and he suggested that I quickly give my parts a scuff with a red scotch pad before base coating.