If this service is up for five years, then it can go down for 15ms and still claim all ten over that period. Which is almost nothing still, but if you needed ten to begin with then maybe it's quite a lot for you.
All I'm saying is - and I think this is what the commenter originally twice above me meant - is that the rate doesn't give you all the information, you at least need a period as well.
99.99999999% uptime is 3 milliseconds of downtime a year. That's not even a TCP retransmission.