I would say between 15-20 min average. Anything longer, doesn't get made around here, because the kids get antsy.
I do clean up while they are finishing as well, because that way, as the others have mentioned; after lunch is diapers, nap and I am free to eat my lunch and have MY time. LoL
I think the only way to cut down on clean up time is to make sure you have an empty dishwasher for the things that can go in, and a sinkful of soapy water to wash the kids dishes as you go. Sorry, no other advice, unless you want to start using paper plates, hahahaha.