By clicking on the server clock in the game you can see when did the game started and it shows what is the maximum length of realm
http://prntscr.com/1ze94o. But it could end at least one week from the time when administrator declare that "The lords of the realm" competition begins and alliance "A" manage to keep Alliance Castle influence for at least 60% territory for 168 hours (depending of the speed mechanics of the game).