You may sometimes see a page like below when you wanted to visit the forum (or other services hosted by the tzmc1 server). Every Thursday (usually in the morning) I update Discourse (the forum software we use). I think Thursdays are best because it’s close to the weekend, so I can fix things if anything breaks. But not too close to the weekend, so the Discourse devs can fix any bugs reported before the weekend. The maintenance usually takes about 30 minutes to complete. The maintenance page in your browser automatically refreshes when the maintenance is complete. There is no need to constantly refresh. 
However, sometimes updates of the operating system require a reboot or service restart. Also, automatic Let’s Encrypt renewals restart the web services automatically as well. In both cases the maintenance happens unscheduled and often lasts less than 5 minutes. This is because I install these updates when they become available in order to stay secure and stable.
Just so you know, in case you were wondering why this sometimes happens 