Finding ways to stay productive in spite of challenges like heat keeping you away from the computer is absolutely critical for a long-term project's survival, so you're doing a good job being resilient! Keep it up!
Similarly, I try to erase the concept of "good season for creativity" and "bad season for creativity" - my goal is to make any season, any time of day, a good time for being creative. I haven't quite worked out a system that lets me be creative during the down times at work, so that's my own challenge. Outside of that, I just try to find ways that keep me engaged and habitually creating. Tutorials, small projects, game jams, the list goes on. I have rewired myself to the point of having a compulsive urge to be creative whenever I have free time, and it's paying dividends.
Have you ever heard of a Game Design Document? It's basically the "recipe" for a game, where you list out all the mechanics, assets, and technical points that go into making the game, with the goal being you can look at that document while sitting at the engine and know exactly what you're going to make. The scan of your notes looks like you have a good start on that. Maybe if you get enough done you can have the bulk of the game "thought out" by the time you can spend the long hours at your computer, so the only thing you'll need to focus on then is overcoming the technical hurdles of making the game come alive.
For further information on Game Design Documents (GDD) see this video: