Letter of Rec Timeline

I asked my PI from last summer if he could write me a letter of recommendation for medical school, but I recently decided that I want to apply next cycle instead of this summer. Is it possible for me to hold onto that letter for next year OR for him to upload it onto TMDAS to be considered for next year's cycle? It can be hard to get into contact with him because he lives in my hometown, not the same city as my university, and I am meeting with him in person to talk about this soon.

I also...

Letter of Rec Timeline