My first task is (obviously) to design what the game will be. I will prioritize by coming up with three features or ideas that I will build the game around, and work hard on implementing those three things first. If the gameplay isn't fun, no matter how much I polish it, it wont still wont be fun.
My first spot of time is only 2 hours long, then I have to run off to a prior engagement for ~3 hours, but I'll have plenty of time after I get back. I'll post my design choice as soon as I come up with it (hopefully within the first hour)