Ah I think I know what's up, Christian. The Offline option won't appear unless you're using Google Chrome as the web browser. The Offline apps suite is actually a Google Chrome plugin, so it cannot be installed into Internet Explorer, FireFox, etc.
The nice thing is, you can set it up on Chrome, then continue to use your other browser if you prefer. But if you're ever stuck without Internet, it'll still be available in Offline mode via Chrome.
Please check it out on Chrome and let me know if that works, thanks!