@Evan *******
nope, just show up. AND Section C-1 is never all that busy. I'd say showing up at 10 or so is fine, no need to get there at the crack of dawn
Works like this; you will apply for the Non-O visa, pay the 2000baht, and they will stamp on your receipt the day you come back with your passport (14 days from the date you apply) to get the Non-O visa and new 90 day stamp inked in.