We value Open Source and make a point to release all our plugins on GitHub under a BSD License.
The WakaTime plugin works for both Sublime Text 2 and Sublime Text 3 and is open source on GitHub.
Install Package Control.
Inside Sublime, select Tools → Command Palette…
Type install, then select Package Control: Install Package and press Enter.
Type wakatime, then select WakaTime and press Enter.
Enter your API Key, then press Enter.
Use Sublime Text like normal and your stats will automatically show on your WakaTime Dashboard.