I have to get this clear from the start; availability is not equal to uptime. You want to have a high availability, but the uptime of the server is not that important. When only one server is used however, availability is somewhat related to uptime (because there is no other server that can handle the requests when the server is down).

But remember that a Windows server in general needs to be rebooted every month (because of new updates). So if the uptime of the web hosting provider’s web servers are longer than a month, it can be an indication of that the web hosting provider is not security aware (but it does not necessarily mean that!).

Patching should of course happen when the load is as low as possible, to not interrupt visitors of your website. Ask the web hosting provider when the apply patches.

Web servers may crash. If/when that (!) happens, what will happen to your website? Will your website go down, and for how long? Or is there another server that can host the websites? Maybe the end-user won’t even notice when a server becomes unavailable (there are different ways to do this, but it usually costs more than $300 per year, which is the price range this article focuses on).