I like warm platens, but don't over do it.
It is POSSIBLE to hit the gel point of plastisol on the screen. I doubt you'll do it, but I have. like Maff said, keep a temp gun handy.
Aluminum platens surrender their heat pretty fast, but mine are all covered with silicone rubber sheeting. If you pass 150° or so (maybe 160°) it is uncomfortable to handle the platens. Too hot to handle is a pretty good test. Stay at that range or under. Use good rhythm and build a habit.
I gelled a plastisol screen on my auto recently, trying to partially cure a mostly waterbased job with just one screen loaded with plastisol. It was right after the second flash, with no cool down station. (DUH. Rookie mistake.) Spoiled a bunch of shirts too, before my chattering unloader caught it. Grrrr.....