Not sure how the plugin tracks AFK but this plugin has some interesting mechanics and wanted to make sure it would properly stop tracking time if a player went afk.

https://www.spigotmc.org/resources/ultraafk-api%E2%95%911-8-1-16-2%E2%95%91the-most-annoying-afk-api-system-for-your-players-%E2%95%91.83275/