Hello Dennis,
The answers to all of your questions basically depend on the amount of racers at that particular event.
What we do is, share a venue with a track. What I mean is, lets say your local track has a regular Saturday night race. Well, if we were to race at that track, we would go in to that already scheduled Saturday night venue and our group would race(with the others, but not against them). Some tracks draw only a handful of regular racers(Gassers and such) to each of their regularly scheduled races, while others draw a very large number of participants for their regularly scheduled races.
So at some tracks/locations, a DHRA event might be only a few hours, while others may be all day long.
Does this help?
If you have any other questions, please feel free to ask me anytime.
Thanks