Depends upon if you are staying at a Universal Lowe's Hotel, sound like your not. So the guests staying onsite get early access to one of the WWoHP areas. I would find out which one they get early access to and go to the other one first. Typically speaking Hogsmeade is smaller than Diagon Alley space wise so it looks more crowded even when it's not. Hogsmeade, looking at all the stores, riding all the rides and going to Olivanders I can get all through it all in 3 hours. Diagon Alley I can spend 6 hours, it has three times as many stores but only has one ride. The HE is not in Diagon Alley and is not part of the early access for onsite park guests, it has a longer wait from Diagon Alley to Hogsmeade, then Hogsmeade to Diagon Alley normally and you will want to ride it both ways as the ride is different in each direction.
You are correct in assuming that Friday will be less crowded at least at first, but if Diagon Alley has the early park access then it might be a bit more crowded at first.