It takes time to affect real change. That’s why you need to plan out each 90 days some sort of goal or experiment, just one or two, that you can give your full attention to. It also forces a prioritization of goals. With only 20 quarters in a 5 year span, you can’t afford to spend those quarters on anything less than full impact initiatives.
However, don’t get stuck in planning mode. Keep a simple top-of-mind tracker that you can use.
I also suggest having your quarters coincide with the calendar, that way you always know where you are/how much time you have left.