There is no timer. My guess is a bit more than one hour?
With my gamer mind, I realise I can move factories as soon as we have enemy form both side. However, there is no room for moving in the later game:
If I move to the enemy , nothing changes;
If I move to the base, the AOE damage my base too;
If I move the base to up or down, half of the enemy would attack the base directly.