CET, I used the "sleep in the quiet side, party in the loud side" for about two years. Please note that the sides are 1) quiet at night, and 2) music at night, quiet in the morning. One year, someone had an alarm clock that went off at 6:30. If you camp in the "quiet at night" side and go to bed at, say, 4AM, don't expect to sleep beyond 6 or 7.

As far as getting a decent spot, if you have a largish tent, it's probably best if you get there before about 4PM. If you have a small tent, there are places to squeeze them in later than that. Of course, they start the festival activities even earlier these days, and I rarely get there before about 5PM, so I could be wrong.