I concur with canuck_traveler about the efficiency at NRT. Flight delays notwithstanding, you shouldn't have an issue. Just be ready to move swiftly and walk around crowds. During a LAX-NRT-SIN round trip MR in Sept, it took me about 30min to deplane, get my new boarding pass, clear thru transit security and find the lounge. They are also extremely efficient with boarding so expect them to start exactly (like, to the second) at the time they state.