I know there is 2 different hardeners for 2021,dcx9 and dcx61 I believe,don't hold me to those numbers,I don't use ppg often,with the dcx9 that stuff really gets really hard,you might be alright if you used the dcx61
Alot of time, it is more preferable to wait awhile and wet sand- buff, lets the paint vent all the solvents....gets hard and USUALLY almost everytime
they will Buff easier...........keep that paper WET--CLEAN....... and have fun, you'll be fine
Its never to late for a cut and buff unless the finish is gone. ppg 2021 is a really good clear and it requires 2 coats. I usually spray a couple extra when I know im going to wet sand. So be carefull and keep the surface wet.