You've got plenty of time. Listen to @Fencer since he actually is in charge of an MSTP, and I am not.
When I was on the interview trail (back before virtual interviews) I remember talking to a student who had worked at Fermilab studying dark matter prior to MD/PhD, and if I remember correctly his PhD research applied his quantitative skills from physics to analyzing protein folding or something similar.
With an additional reminder to listen to those who know more than I do, I would say that as long as 1) you know and understand your research, and 2) you can speak to why you want to do MD/PhD and how you want to apply your research skills there, you should be fine.