The following links provide detailed explanations of how to use convenience store and post office ATM machines.
The closest Seven-Eleven to the ANA Meeting venue can be found here just behind the NHK building across the street from the ANA. Open 24 hours.
The closest Post Office is here - a two min. walk across the street from the ANA Hotel inside the NHK Building. The ATM machines are open from 9:00 to 17:30 on weekdays, 9:00 to 17:00 on Saturdays and closed on Sundays and public holidays.