Maintain 99.999 up time

Often we hear or request to keep services up & running for 99.999 time.  How much maintenance window this gives if we have to maintain service uptime 99.999 time?

Its a simple math calculation ( 365 * 24 * 3600 ) = 31536000 seconds (not considering 365.25  or leap years)

To keep it 99.999%, we have a maintenance window 315.36 seconds, this gives roughly 5 minutes 15 seconds.  

Seconds in an hour  3600
Seconds in a day  86,400

Seconds in a week (7 * 24 * 3600 ) = 604800