Could you look at possibly doing a meal about 6-7pm on the Saturday evening and then those who want to go out can go out after? The nightlife in Birmingham doesn't really get going until 10pm anyway.
In my opinion lets just keep it simple. We can book a table for a meal for Saturday night and if people want to go out they can. We could always go bowling or something similar earlier on Saturday as thats not overly expensive and we can still make a weekend out of it