The WakaTime RubyMine plugin is open-source on GitHub.
Inside RubyMine, select Preferences → Plugins → Browse Repositories….
Search for wakatime.
Click the green Install Plugin button and confirm the installation.
Enter your API key
, then click Save.
Use RubyMine like you normally do and your coding activity will be displayed on your WakaTime Dashboard.
The plugin will be kept up-to-date automatically.
Inside RubyMine, select Preferences → Plugins.
Search for WakaTime.
Click the Uninstall plugin button and confirm the uninstalling.