I like that Dean is a catastrophist and an over-thinker. I am as well.
I am always haunted by what could go wrong.
To me though, 3:30 (or 90 minutes from whenever machine selection time ends up being) seems fine for last quarter. Nobody in that particular field is going to be playing a full-out game at that time because, for the minority of Friday players even *capable* of that kind of game, doing so wouldn't make any sense (no sense that I can see at least).
Strategy for Friday is to run boards, since the only purpose of scores that day is to qualify for Saturday, and a run-board kill screen will be more than enough to do the job. It would be a waste of energy to go all out, since an "all out" score would be overkill and won't get you a spot on the tournament leaderboard.
So, if there is no hardcore shredding going on (and there shouldn't be), all machines will be clear by 5:15 or :30 at the latest (it's 1 hour 45 to 2 hours for basic kill screen, in my experience), and the majority clear before that. And not every machine has to be clear for the process to at least begin. Vincent will just point to a red one and be done with it!
There's going to be 22 machines, and 10-30 Friday players. We SHOULD be okay...
It's also important to remember that Jourdan/Richie may have specific reasons for setting the machine-selection time at 5:00 PM.
I do like the 8:00 PM suggestion though, or even 7:00. That 2-3 hour shift would make a big difference in the quality of the Friday tourney, without making a difference to the Top 12 players. (Nobody is going to bed before 8:00 right??)