One hour equates to 99.86 % uptime. Many hosts publish an uptime of 99.99% which would be 4 minutes of down-time per month. As long as you don't consider updates to your server as down-time, then 99.99% is achievable. However, if you include all down-time, then 99.99% is going to be difficult to achieve. One reboot after an update will use up that 4 minutes. I would say 15 minutes of down-time, inclusive of maintenance, is more realistic. This would be 99.97% up-time,