Yes guests are allowed. That's a reasonable assumption for ending time, but it depends on the number of people who attend. The last time we ran at GPK we averaged 23 participants and were out of there typically by 9:30. Hopefully that helps you gauge it?
BMW 325I E30 Chumpcar Race Car
BMW 540iT M-Sport (New Family Hauler)
BMW 428i Maranello BMW company car