Last night I didn't get a lot of the documentation wrote up, but I did pin down the entire mechanics of the game, screen flow chart and interface design of the game.
I've decided (if time permitting) that there may be two modes: complete before the time runs out and get the fastest time. I couldn't decide which would give the better gaming experience so I decided that creating both and testing both will help to decide this.
Only drafting left to do is the GUI at during the main game. I'll use simple menu designs at the moment and just concentrate on getting it all fleshed out into a working basic prototype.
It should be interesting trying to do this whilst learning the tool.