I would suggest taking the same shinkansen only as far as Shinagawa station and connecting to the same Narita Express there. Arrive at Shinagawa at 10:03, depart at 10:23. You'd have the same 20 minutes for the change but at a MUCH simpler and easier station to navigate. The Narita Express is the same one you would be catching at Tokyo. You'd just be getting on one station earlier. It then goes through Tokyo on the way to NRT.
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