When it announces that it's going to restart in 15 minutes to complete windows updates. at 10:15. And it's the server that hosts the virtual server with SIMS installed.

I had thought I had prevented disaster using this guide:

http://www.redmondpie.com/how-to-stop-windows-8-updates-from-force-restarting-your-pc/

and then running gpupdate /force

However, this turned out to be a false hope, as a phone call from reception to tell me that SIMS wasn't accessible lead to a cold sweat and realisation that, yep, the server had decided to restart itself. After many promises of violence against the person at Microsoft who thought it was a really fantastic idea to take control of a server's restart time away from the administrator of the system, 20 minutes later all is back up and running.

For future reference, this would appear to be a better bet to prevent Microsoft from ruining your day:

http://blog.powerbiz.net.au/fixes/stop-windows-server-2012-and-windows-8-from-automatically-rebooting-the-server-after-logging-in/