My battle plan is as follows;

Hour 1: mess around to think of an idea *done*
Hour 3: Have a tile map loading from the editor Tiled with a basic set of tiles.
Hour 5: Have tanks appearing on the map, constructed by a factory (factory pattern).
Hour 6: Have tanks shooting at each other, and using the basic pathfinding my framework includes.
Hour 10: Have selection of single or multiple items working.
Hour 12: Have user placement of buildings on the map.
Hour 10: Mock up of basic GUI elements completed.
Hour 12: C&C style building of stuff and then placing it works.

By that time ill be in a position to plan the next few stages. I have left 6 hours in the first day for contingency, in the hope that day 2 can be mostly focused on content creation.