Stain protectors are normally sprayed on to the clean carpet, after cleaning whilst damp so will always extend drying tiimes.
As Clinton says the protector needs to cure, takes upto 12 hours i believe, so ideally the room should be kept unused.
A carpet left in high in alkali will effect the protector sticking to it, so always acid rinse, on new carpets i was told to mist the carpet with an acidic rinse to help the protector stick.
Mark