Did you notice much variance between the schools?
I do not put it past some of these schools doing weird stuff to try and skew their kids' times.
Turns out (or confirms?) - that I'm an idiot. There was a site that already had this info. You can look up the difference for Combine vs Pro Day by event, year, school, etc.
https://nflcombineresults.com/prodaycompare
A couple schools 40 time differences:
Overall +.042
Miami +.035
Alabama +.035
LSU +.042
FSU +.032
Florida -.036 (seems strange)
Penn St +.070
VT +.077
Penn St & VT times matches up with the "fast track" skewing 40 times theory