Here is a screen shot of a poll from my DA:

The most important thing I (or any photog) have to keep in mind is we are at a convention. People are rushing from here to there so we should pay extra attention on how long a shoot might take. Don't be over ambitious trying to finish three 2-hours shoots in 1 day or spending 4 hours for one shoot.
At-con photo-shoots have a totally different set of rules.
Just another self-reminder. :)