If you are very new to exercise then 2 hours in one day could be a bit much to start with, but you can always go along and see what you think. Finn is right, find what you enjoy and stick with that, and if you find it too difficult to start with there is no shame in taking a break during the class. I've done it myself in the past, and no-one seemed to look down on me.
Try to increase your general fitness in the next few weeks before you start by walking or dancing to music etc and you will find that you enjoy it even more.
Another thing, from what I've heard, if you are doing 2 hours of cardio exercise with little or no break in between you will find that your body starts to burn muscle to get energy, so try to take some light snacks or energy drink to eat/drink between classes so that your body has the energy it needs to keep going. If this is wrong I'm sure others will correct me.
Good luck on your new exercise regime - I hope you enjoy it!