It'll be all but needed. The land is going to be packed and there will not be anywhere close to enough time for anyone to make it through HE, Gringotts, Ollivanders, and still have enough time to browse the shops/ see the shows. Also, factoring in the down times that will most likely happen with both new attractions. I think 10 should be the gold standard for them until about early August. Then hike it back down to 6 or 7.