Depends on what you're doing, I would guess.....batch of heavily oiled lamb chops, the temp might go up for a time.....
15+ lbs. brisket, yes it will drop from the cold meat mass going on.................
I try to just plan the drop a little ahead & start off a bit high to account for what will happen........if it's a large piece like pork butt, then you're in for the long haul & it's not going to be an exact timing thing anyway......I've tried to get two identical setups & they still have come out 1&1/2 hrs apart........the meat dictates the rules.....................
A thing to do in the way of gaining experience with these things is try to allow enough time to not get nervous & just watch & observe what happens.......make an adjustment, notice what happens, make another, if needed, watch what happens......it will get to be second nature much sooner than you think......it's a Weber!!!!!!