In the Army, when does time on station start?

I know this seems simple, but the question is, does it start the day I sign in to the post? From the day I start to in-process the installation? The unit? I want out of this assignment, and I am looking at minimums, and this is the one I am caught on. I am not boo hoo about it. I have been to other units and loved it, but this one has a whole lot of "Paper NCOs" and I refuse to partake in training dirt-bags to be dirt-bag NCOs. I know its sad as an NCO I do not know this, but I am seeking out the answer from others with more knowledge than I possess.