I went to USJ 2 Fridays ago, during Halloween. If you're not taking any extreme roller coasters like me, then no need for express pass. The roller coasters are 2~3hrs queue. But if you are going during non-Halloween season then perhaps no need express pass too.
I reached at 8am and the park was already open, so headed straight for Harry Potter, no need for timed entry, queue was less than 40mins. Then made my way around the other attractions. By noon i was 80% done so i started queuing for the Halloween Mazes. Most of them start at 12noon, and i didn't know some needed timed entry so i could only enter 2. Around 5pm, i shopped in Harry Potter world and did the Wand Experience(10mins queue) then went out to see the Zombies which start at 6pm. This is the mistake i made because Death Eater show(also 6pm) in Harry Potter World requires a ticket so once i exited the area i couldn't enter again.
But the Zombies were really good too....i thought there would be an opening show somewhere but instead of a show, they just descended into the crowds from all directions and people were just screaming and not knowing why. Then i realised the Halloween Mazes which required a timed entry earlier were open to public again, so i started queuing. Quite honestly, there are too many things to see during Halloween but i was too tired to finish.