The "trick" to dealing with combined classes (where one set of kids only meets for part of the time, while the other set of kids meets full time) is to instruct everyone on the common days, and let them work on their own on the "split days". The "way" to do this is to make your assignments in such a way that they have to problem solve (I have mine write thesis statements to declare what their intent is...we are just learning that now in a beginning art class). When they take ownership of the task at hand, they will try to make the work more meaningful to THEM and then they will work on their own time to finish it. I would keep the deadline fixed for both groups, and encourage both groups to use their time wisely, and to work on it on their own time as well. Also, the other "trick" is to make the assignments fool proof, in that even if you don't have enough time to finish it, it will still look good. Over my 35 years of teaching, I have seen every combination going with classes, including two classes in one room with two teachers, and this exact MTF vs TTH thing. You can make it work, and don't beat yourself up over it...obviously the powers that be aren't worried about outcome.