I always just split the difference on the temperature, start checking on the one the is supposed to have a higher temp at the scheduled time, but leave it in a little longer, and start check in on the one with the lower time 5 or 10 minutes early and remove them both when they seem done. The important thing is making sure that the meat is cooked adequately, if it started out raw. In lots of casseroles the meat is cooked first, so you don't have to worry about that.
This works fine for most things; cooking is very forgiving. It does not work too well for baking things like cakes..
Edited by: ROBBIEB7 at: 4/21/2013 (18:55)