Hello JanLou70,
Welcome to the Apple Support Communities. From your post, Do Not Disturb continues to stay on even when scheduled to turn off. We'll do what we can to help.
Do you have any other Focus settings that turn on after the schedule? If so, check the link you posted from to make sure there are no conflicting schedules.
Verify the schedule in Do Not Disturb if you had to change any settings. Even if you didn't make any changes, restart the iPhone before the next Do Not Disturb schedule: Restart your iPhone
If it's still not turning off like it's supposed to, reach out to Apple directly here: Get Support
Enjoy.