You don't want to start earlier than noon on the first day; half the people won't be there yet. But you should have a couple things going on for those who *are* already at the con; mug-a-guests are good first day events as they reward those who got there early.

Either a Mist or a Movie Screening traditionally goes after Opening Ceremonies...partly becuase both often take longer than the 75 minutes usually alloted to a panel, and also because you've already got all the A/V equiptment set up from Opening Ceremonies. The first proto-Blue Mug, in 2002, happened opposite a MiST session, btw. Blue Mugs are another traditionally evening event, and if your convention is three days, it pretty much has to be the first night. Same reason that VA seminar (if you are having one) and the first set of Radio Play auditions ought to be on the first day.

...And yes, the "set-up starts at 10 am" thing in the art room IS an hour before reg opens. Help is usually needed to set up the actual display boards and table arrangements before the artists have anything to set their work up *on*. If you can, you actually want that done earlier; the night before, if you can manage it. That requires having both the supplies and use of the room. Check with your hotel staff to see if they are amicable to letting you set things up the night before you actually have use of the room.