There are two things that Japan must consider: Not only when to attack, but which victory cities to go for. In my groups games, Japan had a mindset of Anniversary or Revised edition, where you think that the removal of an Allied player wins you the game. This is no longer the case!
In Game 1, Japan crushed the UK and China, but had no follow up plan to get the last and crucial victory city. American out maneuvered them and their mainland gains slowly unraveled.
In Game 2, Japan focused on crushing Australia. They got a foothold on J1 in Western Australia, and on Turn 2 had landed most of its planes there with more transports. Sure ANZAC was thoroughly crushed, but they were never able to beat down UK and eventually America overtook them.
Both times Japan didn’t have that second bit of planning, where they consider which victory cities will win them the game. You have to have this in mind from the outset, or else you’ll find yourself out of position and lose. On Game 2, Japan was collecting 72 IPCs, but had squandered its starting navy and was facing a combined UK/China assault that had regained all of the starting Chinese territories.
So what victory cities do you focus on? I assume Shanghai, Hong Kong, Tokyo, and Manila will be taken, which leaves 4 left.
So which do you find it better to focus on? Calcutta and then Sydney, a mostly avoid America plan? Do you go for Calcutta and Honolulu, leaving ANZAC to do whatever? Is leaving the UK player alone viable at all, going instead for Honolulu and Sydney?