Originally Posted by tide
A counterpoint: it took me exactly 8 minutes to clear outbound immigration at 10am in the morning at T2 North entrance a couple days ago. This was on Aug 30, one day after school started in Japan.
Yep - The lines out of Tokyo can sometimes be short. But don't count on it. And don't count on being able to predict which days are going to be "long queue" days at Narita airport.
You can sometimes expect things to be relatively quiet at the airport - on a regular business & school day in the middle of the week - but discover that they don't have people at very many counters for the immigration check. This means that you can be in a long line of people who have to show their passports before being allowed to leave the country.
Rule of thumb for international flights out of Narita = Aim to be in line at the check in desks 2 hours before your departure time. If you can use the business class or first class check in counters, then 90 minutes is OK.
Any less than that is not advisable.