This is a Hipchat integration, which sends a message to a room once a message in the format of hh:mm gets sent to the room. It will convert the input time into specific timezone formats, displaying the offset from the user timezone. The target timezones are configurable trough the integration config.
To install the integration, use the URL https://world-time-hipchat.herokuapp.com
as addon descriptor in your HipChat instance. The integration is currently not available through the Atlassian store.