Wait, I read what he was looking at wrong (it's been a loooooong day, and it's still going... at least for the next 5 minutes while I type this up...
There is no way to set a "max reply" time, there is no "auto close after X ammount of time" feature in the UBB, nor has there ever been one to my recollection, at least not in .T7.
The feature I was referencing in my post was the Max Edit/Max Delete timeframes.