I do not know much about computers, so I can not provide things like that. I do however have an idea...
break up the tactics screen into 5 sections (1 in each corner and 1 inthe middle for the citadel owner). Each corner is for an order.
The capture timer (like when you capture a city) would also be used. This timer would incorperate the time to knock down the wall, move to the citadel and capture it. This would be how much time the defending order has to defend it. If the timer runs out, the order gets it. If the timer for the next round runs out, then the defending order survives the first round of enemies.
That is the only thing that I can think of, splitting up the screen and all.