During the Leap Day event in 2012, we were able to park hop until 8pm-ish, when they started closing the gates on-and-off, and it was an hour-long wait to get back into DL from DCA.
I believe last year's event was a bit less busy, but, honestly, I don't recall if they closed the gates or not (I wasn't there).
So, this is all a long way of saying, in my opinion, if you leave around 4pm to set up your hotel room, and come right back, you'll likely be okay. However, if you leave at 4pm, set up your hotel room, go have dinner off-site, maybe sneak in dessert or a drink somewhere else, and don't get back to the gates until later, you could be risking a LONG wait to get back in, *if* you get back in at all. Somehow, when I take 4pm breaks, it always takes me f.o.r.e.v.e.r to get back to the parks, LOL.