After playing a few games, this turned out:
If Japan wait until turn 3 to attack, the allies will block all the routes.
US ships will be in seazones 19, 18 and 17, with subs in 16 and bombers on Guam, Wake and Midway.
UK/ANZAC ships will be in seazones 37, 43, 44, 45 and possibel 46.
This mean that new trannies from Japan cannot reach Phillipines or any other location below the 19-16 line.
It also means that the tranny stack outside FIC or Caroline cannot reach all of East Indies.
After T2 UK collect 37 IPC, ANZAC collect 15 IPC and US 22 IPC against Japans 32 IPC. Even if China is down, the Allies have the upper hand.
Basically this will slow down Japan so much, that the whole campaign might be in jeopardy.
As I see it, Japans best bet is a T2 attack. T1 is too early and T3 is too late, unless we find a counter to the allies blockade.