Is 4 days too late for a LOR?

One of my professors didn’t submit the LOR like he promised and hasn’t been replying to my emails since the deadline. I asked around and got one more professor but they said the earliest they could get it in is this Friday (4 days after the deadline). The admissions committee has told me they accept late letters but it is rolling admissions. Will this significantly affect my application chances? Should I find a backup for my backup?