It's ready when it doesn't "string up" when you touch it with your finger.

Keep in mind that although you don't want to gob it on, a thin layer of UH actually has to be thick enough for the lace to grab on to. Until Debbie showed me how much to use in Vegas I couldn't get the lace to stick to it for anything. "Thin" in this case doesn't mean "as thin as possible".

Also, if you want UH to dry very quickly all you have to do is "smear" it with the brush or your finger right after you apply.