I'm not sure when it opens, but I do know it closes at 9:30pm on weekdays. I'm not as sure about weekends, but it should be around the same. From what I remember it should be open almost all day.
http://www.sandiegobadminton.org/schedule.html A lot of people around SD call it the FED too. hehee hopefully, that helps ya out.
Check out this, if that helps. I placed a few links and try to keep it up-to-date. http://groups.google.com/group/sdbadminton