How long might blockade take to force surrender?

How long would the blockade have to last before Japan surrendered?

There is no fixed timetable; surrender becomes likely after the heavy fleet is defeated, carrier strikes reach the home islands, and trade and supplies can no longer get through.

No fixed number of weeks or months follows from the scenario. The decisive conditions would be the destruction of Japan's heavy fleet, carrier attacks on land targets, and the loss of incoming trade and supplies. Fuel and sugar may already have been rationed in 1939, while the severity of food pressure would depend on whether the blockade reached fishing vessels and coastal shipping. Once those conditions held, Japan would have to decide how long it wished to continue without a realistic means to break the blockade. Surrender is therefore a political response to compounding military and economic isolation rather than an automatic date on a logistics chart.