At about 8am GMT, we have to reboot the server, in order to add a beta version of our multiplayer notification system, which will be finished in the next update. Sorry if the downtime messes up your multiplayer games, it will only affect you if you are online at that time, it shouldn't be a problem for games with longer timers.
On the plus side, the notifications should be mostly functional from tomo. They will only be in English and we may have some bugs to iron out but this is why we're getting them live well before the next update. Let us know if you see them misbehaving, thanks!