Was the slab itself wet when you pulled the bins or just the bins? I'm asking because I had the same thing happen but it turned out my shed roof was leaking right onto the stack, not the concrete. If it really is the slab sweating then I need to rethink how I store mine.

I did this on a 9 unit townhome run in Meridian last spring. My lead guy was crushing it on paper but he was also the one fixing the new kid's mistakes on the back end, so his times looked worse than they were. What I did was write down not just the install time but the callbacks per unit, and the lead guy had 2 callbacks out of 9 while the fast kid had 6. Speed per box stopped meaning much after that. The quiet kid was fast because he was skipping shims and rushing the reveals, and it all came back on the punch list. My advice is track the whole job, not just the stopwatch part.