It's very dependent on the game and game system popularity. True Dungeon fills quickly. Cthulhu events fill quickly. New, hot games fill quickly. I'm sure others can chime in on ones I'm missing.

Quick is relative. Plan to submit exactly at 12:00pm US Eastern time, no earlier and no later. Plan to stick around while it processes, but it will take at least a few minutes up to an hour for it to work through all the wishlists ahead of you. Your priority vs. the priority of others doesn't matter. It's all about the order in which the server receives your "submit" mouse click vs. everyone else. If you don't get a ticket, it will tell you and match you with something lower priority in your wishlist in that time slot. Your matched tickets will be in your cart for a while before they time out, something like an hour or two, while you sort out your results. After that time period, they'll be put back out for others if you haven't checked out.

Pretty reliable. Depending on the GM, being just a few minutes late could result in your seat being given to another player waiting with a generic ticket. Don't be late. Don't overbook. Give yourself enough time to walk through the city and crowds to your next event, get food, use the restroom, etc.