Climate change is a function of expanding human population and increases in petro carbon products usage. The solution is in reducing one’s carbon footprint legacy, by that I mean limiting one’s production of more humans.
Now this idea isn’t realistic so I believe any stop gap efforts to limit/reduce carbon use will be futile. Folks’ conscience might be eased with the “I’m taking this avenue to reduce my footprint” but there won’t be any sustained decline in pollutants overall, human number expansion is inevitable. The exception to this is a fast transmission disease, always fatal, for which a cure or prevention cannot be achieved soon enough. Of course, non-density dependent population reduction can be achieved by a meteor impact, mega volcanoes or some other catastrophe.
Live close to where you work. Generally, you use more gas going to and from work than anything else. Plus, they don't pay you for windshield time to the office. I've lived in super rural areas, the suburbs and "in the city".
If you care about your footprint, it's tough to have a small one in a rural setting and work away from the home. The suburbs can be almost as tough.
A small house is helpful, insulate the attic, get better windows, get a more efficient heat source.
I would not use a timer. I'd be very concerned about the growth of bacteria, specifically, Legionnaire's Disease Bacteria (LDG), during times the heater is off. Hot water needs to be constantly maintained above a certain temperature to be safe. Best just to have the heater well insulated, and let its built-in thermostat do its thing.
Check this out: https://www.osha.gov/dts/osta/otm/legionnaires/hotwater.html
Excerpt: "Temperatures maintained below 60°C (140°F) encourage growth of LDB and other microorganisms."