I work at a big company in Silicon Valley. Our "happy hours" take place during work hours, usually from 3-5pm. However most people use it as an excuse to leave work early to beat traffic on 101/280 (but let's face it, no one beats traffic here). I'm 26 while most of my coworkers are in their 40's and 50's. I don't think anyone cares if I go or not.