Tired of Body Filler Hardening Too Quickly?

And I have found the best time to shoot is right at daylight, when the dew is still on to keep the dust down, and no bugs.
I have everything prepped the night before, so all I have to do is wipe the car down, fill the paint cup. Yes I am shooting in a garage.
Back in the late 89s early 90s I used 2 different guys for body/ paint. One guy was a case a day beer drinker but the best body man ever. Or I should say as good as the best. He was wayyyyy out in the stcks. Anyway, he said best time to shoot single stage was when there was some humidity. He could lay it down as shiney as anyones best bc/cc.