you can get a wristband any time you want. they give them out prior to doors opening. beginning at 5 they ask you to line up by wristband to keep the line order in control. Then they start letting people in to swipe their card and get an official wristband for north or south side of the floor.
once all wrist banded people in line through the door, you can literally walk up and go in no GA line wristband is even needed. Its only prior to doors opening that you need it.
not random. when the doors open they start at the beginning of the line.
be there at 4 to "prepare the GA line, get in order", doors dont really open until 6. then you go in and sit around until 8:15... so if you wont want to waste all afternoon. dont go and get a wristband, because it means standing in line for hours.
you can walk in at 7pm and be 2nd row on the floor. no worries.
i've gone to boston 1 and 2 and spent over 12 hours waiting in GA, and got front row on the rail (great), but tonight im going with my wife and we are going to walk in at 7pm and still be close enough to see the whites of thier eyes. she doenst want to stand around all day either.