Are you wetting the screen down a little with a damp sponge and some water / solution mix? I use about 90% water and 10% 409 cleaner. I know that some companies have their own solution but this works for me. It helps keep you emulsion from sucking all of the water out of the ink. I use primarily speedball wb and I almost never have any major issues with drying on the screen as long as my screen is well exposed and I use this method.