With 13 months, you can renew your certificate once per year and still have one month of buffer time. But in 2 or 3 years the maximum length might be tightened

With 13 months, you can renew your certificate once per year and still have one month of buffer time. But in 2 or 3 years the maximum length might be tightened even further. At least there has been such a trend of length decreases in the past.