Emacs has a built-in world clock! (of course)
It is handy, for example if you collaborate and set up conference calls with people in different timezones.
To run the command: M-x display-time-world
To customize the locations for which you want to see the local datetime, there is the variable display-time-world-list.
;; findout timezone location strings at http://worldtime.io
(setq display-time-world-list '(("Europe/Berlin" "Munich")
("America/Los_Angeles" "Berkeley")
("China/Hong_Kong" "Hong Kong")
("America/Montreal" "Montreal")
("America/New_York" "New York")
("Europe/London" "London")
))To findout the actual names for different timezone locations, I searched on http://worldtime.io.