Sometimes I have a hard time with it too. For me, Saturday 11/07/09 was the first day I qualified for retirement. But since that fell on a weekend, I made Monday 11/09/09 my last day of work just so that there wouldn't be any question about my eligibility. But then, is my retirement date Monday 11/09/09, which was my last day of work, or Tuesday, 11/10/09, my first day of no work?
Oh well! This is not such a bad problem to have.
By the way, whenever it was, CONGRATULATIONS on your Retire-a-versary!