What kind of thing are they speaking on and what kind of audience (I know they are going to be lawyers but we come in many different guises haha)?
Timing will be tight if you're having a full three course with coffee after. Having seen the times, the last thing you want is to have the last speech rushed (maybe have a word with the speakers about the timing).
A leisurely coffee is always good after dinner as well to have time to chat to others.
I always find people who often work late hours often turn up late as well so give a gap at the beginning for tea and coffee and introductions for a scheduled start say quarter of an hour after you advertise it (then you're hopefully at least one step ahead).
If you serve tea and coffee at the tables then you have them sat and ready to listen for the first speech at, say 8pm.
Give 30mins then start serving starter. 5 to serve, 20 mins to eat, 5 for clear up, 30 mins for main, 5 to clear, 20 mins for dessert. = circa 2 hours = 10pm.
Then coffee is served for the final 30 min speech giving about 30 mins for people to wander and chat then leave.