Please note that exchange offices may have different opening times (check this article)
At the office, fill out the form at your disposal there and show the entry stamp that is on your passport.When exchanging your voucher you will have to decide on the date you want to start using your pass.
This date has to be within 30 days of the exchange. Once it is validated you will be able to use your pass starting on the date you have chosen for the consecutive number of days for which your pass is valid.
WHEN SHOULD I ACTIVATE MY JAPAN RAIL PASS ?
The exchange date does not have to be the starting date. You can choose your starting date when you exchange your voucher, that date cannot exceed 30 days after the exchange. If you hold a 1-week Japan Rail Pass you should be careful about your starting date. On a tight schedule, it is better to use a day rather than to waste one.