I think it means that your class will be on Friday, 20 January 2017. But it can be rescheduled again if your professor tell you in advance. So if your professor doesn't tell you anything about it, your class will be on Friday 20 January. CMIIW

I would check with your professor. Usually a "make up" class is an extra day that you will use if a normally scheduled class is missed (a normally scheduled class gets cancelled or you are too sick to go to class one day). But if you go to every class, you don't need the make up class. This program has scheduled the make up class for January 20 as a default. However, if your professor wants to have the make up for some other day, she/he can schedule it for wherever. So, I would assume you *don't* have class on 1/20, unless you miss a class. If you miss a class, you *do* have a class on 1/20, unless your professor tells you otherwise. But I'd ask to make sure.

It means your class will be on 20th January 2017, unless your professor tells you a different date. If you do not hear anything from your professor, then your class will be held on 20th January.