I do pretty much the same thing as djz, but there is one thing that I want to add. Try as hard as you can to get something very basic and playable as soon as you can. Once you have something playable, whenever you get discouraged you can just play it for a few minutes, and think to yourself how cool it is that you MADE that. Really helps me to stay motivated to dedicate some of my free time to completing it.

You'll need to prioritise your time.

My suggestions are
Only go to the gym every second day, freeing up 1.5hrs.
Cook enough to last for 2 days, so that every second day you can eat leftovers quickly.
Sleep for 1hr less every second day.

So in total you can free up about 3 to 3.5 hrs every second day, which you can spend programming :)

I agree that prioritising in this way would free up some extra time but what you're suggesting is to prioritise at the cost of health and fitness. I personally dont think that's a wise decision. It's no good being a brilliant programmer if your ill all the time or sleep deprived to the point your useless.

Anyway, nice suggestion.