Originally Posted by railroadtycoon
I often arrive at the Airport 2-3 hours early on international flights out.
Check-in, security, exit immigration, can be long at times.
Since it takes 1-2hrs to get to Narita Airport from Tokyo, I'd leave somewhere around 11am.
For the CX 15:40 flight (which I've been on many many times) I'd take the 13:03 NEX out of Tokyo station (or the 12:42 out of Shinjuku). Puts you at the airport at 13:57, almost two hours before your flight. Plenty of time.