if you "feel" anything at all, it may be a percieved raise in body temperature, and like Airwalk said, your tummy may feel a little off. and unless you know exact dosage in whatever you're taking, there's no way to tell how much you're getting. are you going to be eating blotter, liquid, gelcaps?
generally speaking you can expect things to start getting interesting within the first hour, and get progressively weirder after that. up at about the 4 hour mark is where you'll most likely level off (from experience and readings elsewhere). however, i've had acid thats come on real strong within a half an hour. and like i said, you can never know for sure how the stuff is going to work until someone has tried it. so ask whoever you're getting it from what to expect: strength, onset etc. my last batch the guy told me take one, you're good, take two, you're fucked. we took two. he wasn't kidding.