We took the San Diego Zoo trip with Grey Line last week--we were told that everyone is picked up at hotels between 8:15 and 8:30ish for most of their tours and taken to the depot where you are directed to your actual tour bus based on your destination. The depot was probably 5 minutes away--not far. Most of the busses didn't leave the depot for their actual destinations until 9:15-9:30. The time went fast--and the depot had vending machines in case you forgot a snack or beverage for the ride.
Yes we used them to go to knotts and to Sea world and were picked up about this time and taken to the depot. There is also a shop in the depot with reasonably cheap snacks, drinks souvenirs etc.
I know we arrived at Knotts before it opened so had chance to look in the shops outside while waiting