I always try to be early as both a cosplayer and a photographer, but I have seen bad behavior on both sides of photoshoots that result in wasting other people's time.
I've been blown off by cosplayers who asked me to shoot them with zero contact, but on the other side of the lens I used to know a person who booked quite a few shoots of other cosplayers at a con then blew them all off because she didn't feel like it (and made excuses to the cosplayers after the con was over). I've also had a photographer ask me to wait around for a half hour so she could come back after another shoot and take pictures of my costume. She did come back and we did shoot, then she never posted any photos and ignored me when I contacted her after six months to ask if they just hadn't been any good (I wanted some kind of closure on it, you know?).
So... yeah. Both sides need to respect other people's time. :/