I annoy myself

Here's a habit I've been trying to break for a while now: I stay at work too late.

Not hours, just five to 15 minutes. Work isn't overtaking my life or cutting into stuff I care about much, I'd just like to have dinner ready a few minutes earlier or get other stuff done before I start cooking or commute when traffic is slightly better. But I can't, because I keep staying at work just a tiny bit longer than I'm obligated to.

I can think of three completely different reasons for this, and if it were just two, I probably wouldn't even mind.

1. It's hard to figure out exactly how long I'm obligated to stay, because my routine after getting to work takes quite a while. This is mostly because I bike, and therefore have to shower and change after getting to work. Add in a trip to the cafeteria for coffee, and all that takes over 15 minutes. In theory I could claim to be working as soon as I first get to my desk, and if I had to I would, but it would seem dishonest to do that regularly if I'm still wearing shorts and a t-shirt. 
2. My job doesn't ask much, so time is the least I can give it. Obviously, it's not very stressful or demanding. So I figure it would be kind of crappy of me to cut corners on my time.
3. If that was it, fair enough, working long hours might be just the price of getting exercise as I commute and keeping my conscience clean. However, I have to admit that the third reason is the real one, as often as not: I procrastinate. I put a task for work off until the last minute and it takes five, or I'm reading an article or blog and decide to finish the article before I go home. 

Now that is stupid. I think procrastinating on leaving work and going home for the day might be taking procrastination just a little bit too far.