Office hours are not consistent in local time either - there are cultural variations. If you want to know what (UTC) times the Chinese guy will be in his office, you need to ask him, not try to predict using offsets from UTC.
In the approximately 10 countries that I work with - they are all available from 9:00 AMsh to 5:00 PMsh. This may be unique to my sector (Energy/Utilities) - but it's pretty much consistent Across Brazil /UK/ Portugal /Germany /Japan/ Singapore /Australia /Malaysia /US /Luxembourg)
I don't work (yet) with anyone in China, so I can't comment on that country.
