We were there at rope drop last July, got our first choice of times, and will do it that way again this July.
But when you pick, choose a time when there's not as much of a chance of thunderstorms. We talked with a woman who had had an afternoon time for her son the day before and it was canceled because of storms. She had to start the whole process again the next day because there's no way to reschedule--you just lose out. Hard to predict, I know, but keep it in mind.