Issue with iPhone Downtime Restrictions

I’ve discovered that my child has found a way to bypass the iPhone’s downtime restrictions. When he gets the prompt asking if he wants "one more minute," he powers off the phone. Upon restarting, the app become accessible for the rest of the day, and the communication limits are lifted as well. It seems the phone treats the apps as if they’ve been approved for full-day access, and I’m unable to reapply the intended limits.

Anyone else experience this? The downtime feature is essentially useless