Hmm...Arthmoor did something a bit like this in Faregyl, didn't he?
In any case, I like that idea, it should provide an extra degree of immersion for the mod. I see what SilentResisdent thinks about (I'm sure he'll like the idea though), and I might have a look at doing that in the near future.
On the door opening/door shutting mechanism though; wouldn't it make more sense for the door to shut as soon as you enter the interior cell? Because if there is a timer, if you immediately exit the interior you might find the door still open when you go back outside, which will then allow you to enter the exterior interior(tongue twister or what) of the fort. And to go back into the fort you'd have to close an already open door...
But otherwise, great idea.