An "early in" will get you admittance at 8am ahead of the general admission throng. But, you're right...get a table and you can set up Friday night ahead of the show. Some good things happen Friday night during setup, and there's usually a program Friday night
The earlier you get there, the more good buys you'll find. But not everyone is looking for the same stuff, so if what you are looking for isn't a "high demand" item, it may sit all day.
One good way to shop a swap meet is to first make a whirlwind tour of ALL of the tables, then go back for a closer look at each table, but still not spend 20 minutes at each table. Then, on a 3rd round you can start to spend more time at each table. But if there is a Hasselblad sitting on a table for $150, you'd best not be studying some off brand $3 enlarging lens for an hour that you aren't even particularly interested in, because super buys don't usually just sit and wait for you. (But!!! Sometimes they do--like my $25 Dagor!).