With the Gymnasium Lehrte Representation Plan you can see if you have any missing or other substitutions and changes for you.
Everything is compact and clearly presented.

With a swipe to the left you can see on the second page all additional information that is otherwise in the header.

After signing in with the normal Proxy Password plan, you'll be giving your class and directly seeing any timetable changes that are important to you.

The app also sends push notification within a few minutes if something has changed for you on the substitution plan.
If you do not want these notifications, you can simply disable them in System Preferences.