As I'm sure you can probably deduce, "a variety of factors" affect emulsion drying time, (humidity surely being one, also temperature, also airflow) but usually it's pretty obvious when the emulsion I use is dry: it's matte and smooth. What I do is set a fan blowing on the wet screens and go do something else for about an hour. This is something a real pro wouldn't do, I think, because the fan will blow dust into the emulsion. Someday I want to build a drying cabinet that blows warm filtered air around screens! For this, I need to take the cabinetmaking course at my local trades college. (Plans on screenprinters.net, maybe.)
Recently Michael Motorcycle had a problem with screens falling apart during a run. My experience with waterbase is that if you do not dry the screens below 50% relative humidity for 3 hours, you do not acheive a total cure of the diazo/emulsion chemistry. They are dry to the touch long before the 3 hours if it is warm, but you run some risk if you just go on feel.
It doesn't matter as much if you are using solvent based inks or plastisols, the stencil has a built in resistance to the inks because the emulsion is essentially waterbased (oil and water don't mix) but if you run into problems with stencils going soft or pinholing with waterbase, it is probably the drying/humidity thing.
I use an old hairdryer I throw in the drying box and a $10 humidity/temp guage from the hardware store. Pro shops use a dehumidifier.
Hey, the fuc@$^@^ing election is over. We lost. Spent the day pulling down signs. Never again. Time to rebuild squeegeeville....bigger and better and faster and smarter.
andy pretty much covered it. i dry my screens with a fan (after coating with ulano QTX), then usually let them sit overnight (under a blanket) before i expose them. there have been a few times where i needed the screen right away, so i dried it for about 2 hours next to a fan, then exposed. it seemed to work fine.