When I was on a monthly prescription the insurance company would let me refill at day 25 (don’t try it on day 24), but they never realized that I was doing it every month and got two months ahead by the end of the year. The big thing is to rotate stock so you use the older pills rather than letting them sit on the shelf while you use the new ones.
This is what I did back when I was taking long-term prescription meds.
This leads to getting 12 fills in a 10-month period, at which point you need to call your doctor and ask about a new prescription, lest you burn through your cache.