Having traveled with YZReef for 2 years and nearly 40 shows, it's my opinion that making the day longer just makes the vendors have to stand around and wait longer. At the end of the day very few people are buying anything and most people just stand around talking waiting for the raffle to end.
As well many vendors would prefer to have AT LEAST 2 hours to get set up. And the earlier you have set-up start the earlier they have to leave their origin.
Just figured I'd throw my opinion in, having been on the other side of things.