Im guessing that its a Pak40 that is responsible for the tank kills? To bad we only have one mortar avvailable in this action.
Remember that if the time runs out and both sides are still present on the map (or a ceasefire is agreed before then), the next turn will have the option for both sides to continue the fighting (with according setup zones etc). We might be able to send more reinforcements by then (a Coy of Inf is currently disrupted and couldent join our initial attack).
So time is not a critical factor, take your time, use your ammo. City fighting can be a real bitch.
Taking terrain and encircling the enemy defensive positions (they can be cleared later) might be a good move. Your choice of course.