After the first extraction, I usually leave about an hour or so for each subsequent pull. After the third pull you're pretty much just getting plant matter, very little of the good stuff. I usually leave it at four pulls.
And no, you're not really going to get much better yields by waiting more than 4-8 hours after the first two pulls, because the first two get the vast majority of the stuff you want. After that, you're basically just getting the little bits that are still stuck in solution.