Here's how /tz will work in HipChat once you have it set up:

HipChat Time Zone Converter and Calculator Demo

Setup Step 1

Log in to HipChat from a web browser and click on the "Integrations" link in the top nav.

Step 2

Select a room to use for /tz from the dropdown on the left. (HipChat won't let you install it for all rooms.) Click on the big blue "Build your own integration" box.

Step 3

Enter in a name for the integration. "Slash TZ" works. Click the "Create" button.

Step 4

Tick the "Add a command" check box, which will reveal the options for the slash command and POST URL fields. Use /tz for the slash command and for the POST URL. Click "Save".

That's it!

Type /tz help into the room you selected in HipChat to get started.