I think happy hour is an interesting phenomenon. When I was in school, happy hour made sense: drinks were cheaper, which in turn, makes you happier (and drunker (which makes you happier)). With work though, happy hour oftentimes does not even include drink or food specials. It's just a time when you can get the hell out of work and get alcohol into your body as soon as possible. A more appropriate title would be "Thank the Lord I Don't Have to go Back to that Desk for Another 10 Hours Hour."
I realize that for most people, happy hour is truly a happy time, but again, that happiness usually stems from not having to be at work coupled with the alcohol. By that account, lunch could also qualify as a mini happy hour (or half-hour). You get to leave work, get some food, relax. That's happy hour right there minus the alcohol.
And if it's the alcohol that makes your hour so happy, why not just sneak some vodka into work and drink from 2-3. Guaranteed that could be one hell of an hour, and quite possibly much more fun than sitting with coworkers who you've just spent the last 10 hours with, trying to make small talk, while not trying to seem like a raging alcoholic (I admit, getting caught drinking vodka at your desk would make you seem more like a raging alcoholic, so you should try and avoid getting caught).
I hope I don't seem to bitter about happy hour, because I'm not at all. I just think it's an intersting cultural phenomenon. In fact, I'm going to go to happy hour today, although I doubt it will last just an hour. See you at 5. . . .