Each conversion has a separate 5 year clock.
However, that is irrelevant for you and you can ignore the conversion clock after age 59-1/2. When you do the conversion, you pay the regular income tax on the converted amount. The 5 year conversion rule says that if you withdraw the converted funds in less than 5 years, you pay a 10% penalty for early withdrawal. But that penalty never applies once you are over age 59-1/2.
