It is a bloody fantastic game. The battles themselves don't take more than 15 - 20 minutes though unless someone is using stalling tactics or both armies spend an inordinate time waiting for the other one to move, however the multiplayer resolves this through the shrines so that if one arny is staying back, the other one can grab the shrine and receive boosts.
A multiplayer battle shouldn't last very long. We can always set the time limit to 30 minutes if necessary.