Where did it go?

In to work at 0800 hrs as normal. Finished at 1830 hrs, also relatively normal. When I go in to the office I like to miss rush hour so it easier to arrive early, finish late. So that is ten and a half hours isn't it. Minus 45 minutes for lunch. Down to nine and three quarters then. So why can't I remember what I actually did today. Slightly worrying. Just in case any bosses read this, I promise it was worth while, whatever IT was.