The Cannock meets normally have an early doors (8am) ride for the locals then the main group ride for a couple of hours. Followed by a break for mince pies and mulled wine (other refreshments are available) back at the car park. After that there is a shorter ride taking in some of the unmarked trails. I have only done the main ride for the last 2 years but definatley worth going just for that alone.
I assume you are not working the following day as it is also a bank holiday so no need to get too back early. It's a long day but worth going.