It kind of also depends on the OS. And before the comments start; As with anything, situation & a bit of luck go a long way.

But Linux based machines can be left enabled for months, some times even years. Windows I Honestly wouldn't trust beyond a few months and even that would seem too much for my own taste.

I reboot my systems monthly most of the time, usually paired with updates. But my main host is Windows serv, which gets daily reboots (power savings, I don't need it on when I sleep), and the VMs on that are frozen & unfrozen so they are on for about a month or more until I do the above.