Tired of Body Filler Hardening Too Quickly?

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.
Use a hot plate to warm the single stage paint up, it will flow like glass.