My opinion/experience only:
Depends on whether you want to wait before or after the door opens. Waiting will happen either way, so it's a matter of timing.
Show up early, and you get out early, as once the line starts to move it will move slowly, but steadily. Show up later and you get out later, and depending on how much later you show you may not get in at all.
I have shown up between 2 and 4 on average, and the line is usually about 3/4 full in the first section, preparing to be broken to the second section. I would not show up later than about 5:30 if I could all help it, but that is my personal guideline based on how quickly things start piling into the adjacent hallway around 4:45 or so.
Do bring a book/tablet/portable game thingy/knitting/etc to keep you busy, or bring a few pre-registered friends.