Boston is typically 14 hours behind Tokyo. When it's 9:00 PM in Tokyo, it's 7:00 AM in Boston. Japan does not observe daylight saving time, but Boston does.
During US daylight saving time (March to November), the difference is 13 hours. During US standard time (November to March), the difference increases to 14 hours.
Optimal meeting window: 7:00 AM - 9:00 AM Boston time (8:00 PM - 10:00 PM Tokyo, or 9:00 PM - 11:00 PM in winter). Early morning Boston catches evening Tokyo.
Boston's universities and research hospitals have extensive partnerships with Japanese institutions, often requiring early morning calls.