When do you dash to the lav during Harry Potter’s latest adventure?  According to www.RunPee.com , a good time is when Harry takes his professor to visit Hagrid, a bit less than two hours into the movie.  RunPee gives you the cue and the gist of what happens while you’re away (tho it’s never a spoiler) so you can piece it together after you’ve gone and refill that 64-ounce drink.  You’ve still got an hour to go, by the way, so sip slowly.  If the soda hits you after you leave, you can check www.WhereToWee.com for the nearest restroom.