What are you saving for? Just convenience or is this for long term prep? Convenience would be about a year with stabil. Long term... in that case do you care if the engine runs a little rough as long as it runs? You can go several years on gas storage with stabil, but starting is hard and it probably wont be smooth running. Keep a selection of cans of starting fluid. When you absolutely need it to start is not the time to find out your gas is a bit old for a finicky engine. BUT, if you are only holding 25gal, you probably aren't looking to try and start an engine after 3 years of hard survival (whatever the cause, but prevents you from acquiring fuel for 3 years). I doubt you wouldn't have already used it up.

If you are dedicated to long term fuel storage, consider keeping simpler engines. Many of the brand new, high tech engines do not like old fuel and the control systems may prevent it from being allowed to start. I "dispose" of my old gas by running it in my 50's era tractor, because it couldn't care less what is in the tank and the carb is super simple to clean if I manage to varnish it up with mistreatment.

All my long term essential equipment is diesel for a reason.