I agree with most of the comments posted:

- the walk is between 12 to 15 min tops (even dodging a starbucks line guy costs you about 2 seconds max

- the NRT flight WILL be boarding when you arrive - they start between 1110 and 1120 depending on load

- checking bags seems very risky

- i have seen doors close on this flight 15 min prior to pushback

- any delay at all, and you are hosed