Japanese pension refund

So I worked in Japan for 4 years as an ALT and was paying into the pension system. I have since left and I know that you can get a partial refund back once you have left the country. Is there a time limit after you have left to apply for this refund? How about if you choose not to exercise this option on the off chance that you might return to Japan in a working capacity in the future. If so, would you just resume pension payments from where you left off?

For the second half of your question... Yes, if you return at some point, even years later - so long as you can reference the pension number or correct name of the firm (if a company paid on your behalf) so that your pension number can be found, you just continue from that point, accumulating additional months paid toward vesting. The time you were away from Japan is excused from the payment requirement. Many years ago, I was gone for 7 years and continued after that absence.