I don't understand how anybody voted for the first option: right after the AO.
The only way Nole could lose the #1 right after the AO is if Roger wins the tournament AND Nole gets knocked out before the semis. How likely is that? Nole has made the semis in the last 10 Grand Slams he's played. It's not reasonable to think he'll lose before the semis in Australia, his favourite Grand Slam. It may happen, but it's unlikely.
If Nole loses in the semis in Australia, Dubai, Indian Wells and Miami, he'll lose 1920 points, even if Andy wins all of those tournaments, or Rafa does, or Roger does, together with Rotterdam (given that he's not playing Miami), they still won't pass him. So I think it's safe to say that Nole will keep the #1 at least until the clay season.
If Nole keeps losing in the semis in Monte Carlo, Madrid, Rome and Roland Garros, he'll lose another 960 points. Then he could be in trouble, but Roger would have to match his beginning of 2012 to pass Nole, and Andy would have to improve his results of 2012 dramatically: like winning Australia, Dubai and Miami and making the semis in Indian Wells, say. Rafa couldn't pass him either, he defends 2000 points and is 6000 points behind Nole.
So even assuming this poor performance by Nole, it doesn't look as if he could lose the #1 before RG.
I think the earliest he could lose it would be after Wimbledon.
But I don't think he will. I think he'll remain #1 all through the year. He's already defended the year-end #1, 2012 was not as good as 2011, so it'll be easier to defend the points, he's learned to deal with the commitments of being #1, there'll be less pressure on him: the pressure will be on Murray, to see whether he can win another grand slam title...All in all, I think 2013 will be an easier year for Nole than 2012.
At least I hope so.