“Nines” can be turned into time, for the purposes of discussions:

            Uptime        Monthly Downtime    Annual Downtime
Five Nines   99.999%             0:00:26              0:05:11
Four Nines   99.99%              0:04:19              0:51:50
Three Nines  99.9%               0:43.12              8:38:24
Two Nines    99%                 7:12:00             86:24:00

This assumes a thirty-day month, at twenty-four hours a day (720 Hours/Month). The annual number is simply twelve times the monthly (there may be some approximation). These figures should provide an idea what a given “nine” provides, though should be validated before writing it into a service level agreement.