Well, the basic game was in place in just 2 hours: cities, missiles, explosions, and multiple waves of difficulty. But getting the rest of it done took a few more hours to get it just right. Probably about 6 hours in total. Not bad.
At some point I may come back and add in bombers or a few other fun little features, but I’m quite happy with the current state of it.
All the source code for it can be found here.