Im a bit retired from clubbing in LA but i can tell you that the key is to meeting the right people. You can find parties that go as late as 6am, 10am, 12pm. I usually left San Diego, which is a 1.5 hour drive, about 11 or 12 cause i knew it would go late. I must warn you though that some of the places these parties take place are a bit sketchy and sometimes you might have to drive to the valley or some sketchy neiborhood downtown LA.