Patrick Arnold said that its best to take it all at once because that way you can be sure to kill all the estrogen, and you only have to clear it all out once a day. He said several lesser doses would lessen the effectiveness (he didn't use those exact words, he said a bunch of science ****, but that was the overall message).
The way I see it for PCT, the more the merrier as far as natural test boosters. Your goal is to get your levels back to normal. Trib, ZMA, long jack and 6oxo all can help do that. I don't know why you'd want to take 6 oxo after 4 weeks of nolva tho. I may be wrong, but I'd think at that point your test should be back to normal.