We have only been to the HP section at Islands of Adventure, so I can't advise on the new section at Universal Studios.
I think probably the best way to take advantage of your time there, if budget allows, is to stay at a Universal hotel so that you have the early admission option. We did not do this, but are considering it for our next trip.
Barring that, the approach that worked for us was to show up early and be in line at park opening, then go directly through the park to the Harry Potter section. Getting in line for either the Forbidden Journey or for Ollivander's Wand Shop is probably your best bet, because the queues for both will get longer and longer as the day goes on.
Getting there first thing, we were able to knock out the Forbidden Journey, the wand shop, the smaller roller coaster a couple of times, walk through the shops, and eat lunch at the Three Broomsticks -- all before noon. We didn't ride the Dueling Dragons coaster but we had time to buy wands and take pictures in Honeydukes candy store and Zonko's Joke Shop.
By noon-1 PM that section of the park was getting very crowded, so it was the perfect time to move on to other things.