If there is rain in the late afternoon or evening, go to WWOHP after the rain ends/before park closing. We did this two weeks ago and it was awesome! We were eating at Jimmy Buffet's when it rained around 6:30 - 7:00 PM. IOA emptied while we ate, and then the rain stopped. We virtually had Potter to ourselves! Both FJ and the dragons were a walk-on, and even the wand shop only had a few folks on the line. Plus, seeing it after sunset was even better than usual.