• Do I have to start at 6:30?
• How does the timing work?
• Can I leave for lunch?
• Can I set up a table?

No.  You may start and stop at any time.  You may run/walk for the full 12 hours, or you may come out for 15 minutes after lunch. 

You cross the timing mat for the first time to start the "clock".  Every time you cross the mat after that counts as one lap. 

You may come and go as you please.  If you decide to go out to lunch, cross the mat to finish a lap, then go get lunch. (If you decide you're done, your lap will be counted that way).  When you come back, bypass the mat and get back on course.  You skip the mat so you DON'T get an extra lap counted.  If you make a mistake, stop by to see the timer who will wipe out one crossing.  Yes, that means your lunch lap is a lot slower than every other lap, but that's what you get when you go eat chili dogs. 

Absolutely.  The northern leg of the Clark Road parking lot is nearly 300' long and parallels the end of all three of the event loops.  Back your car or truck up to the guardrail (It used to be chain, but changes), set your table or tent up, and enjoy.  There are generally plenty of places to do this.  And if there are no spots left to park right there, there is plenty of space nearby to set up and be left alone.