How long would synthetic-fuel plants take to build?

How long would Japan have needed to build and operate a substantial synthetic-fuel industry?

About two years for initial plants and operating experience, making a 1936-37 start potentially useful before the later oil embargo.

The estimate is roughly two years to build plants, bring them into service, and acquire working experience. Yonai and other officers were already pressing the issue before 1937, so starting in 1936 or 1937 could have produced useful capacity before the later oil crisis. Synthetic fuel was costly and consumed enormous amounts of coal, but even limited production would reduce exposure to an import cutoff. Its strategic value was time and flexibility rather than cheap or complete energy independence.