I posted a BOJ preview here earlier:

And I also noted that there is no firmly scheduled time for their announcement, once the sake runs out I suppose.

0230 to 0330 GMT GMT is a good bet. More detail here

A little more preview now, this via Rabo:

BOJ could further cement its dovishness

  • Given that the JPY is inclined to be tuned to international events and geopolitics rather than the domestic economy, this may not be sufficient to push USD/JPY significantly higher.

due to the JPY's function as a safe haven, its performance tends to be more influenced by the general tone of risk appetite. As a consequence the outlook for USD/JPY is likely to be more heavily bias by whether or not the market see the potential for some sort of resolution in the trade wars between the US and China and potentially by news surrounding Iran.