On the U2.com press releases, they always list Japan after Australia, so presumably the shows there will occur in early April after the Australian dates. There is a 2 week gap between Buenos Aires' rumored dates and the confirmed date for Auckland, so it could happen then, but I doubt it.
I would guess on 2-3 shows total there, as Zoo TV Japan had 2 shows at the Tokyo Dome and Popmart had 1 show in Tokyo and 1 in Osaka. Perhaps this time Tokyo may get 2 shows and Osaka 1.