If you want to leave earlier than half past ten:
1. Turn up before ten, whoever is equipment should be there from half nine anyway.
2. Get your boat and gear and put it on the trailer, no one else should be doing it for you.
3. When everyone who turned up on time has their gear on the bus, leave.
4. At the river, do the car drop first, if you have turned up early get changed and when the bus gets there do the car drop. While that is going on people should be getting changed and getting the boats off the trailer and down to the get in. By the time the bus has returned with the drivers you should be nearly ready to go. People split into groups and rescue assigned.
I know this will just be ignored but it works and is very effective at getting trips off on time.