Hi there Ianmclein,
We know you mentioned not wanting to be directed to update your software, but we want to be sure we're on the same page since an update was recently released that could potentially help with the behavior you're seeing in Screen Time. Do you see iPadOS 16.3.1 listed next to Software Version in Settings > General > About? If not, you'll want to update with these steps: Update your iPhone or iPad - Apple Support
If you have updated and your Screen Time settings still aren't saving as expected, you'll want to make sure you're following these steps to set your Downtime schedule: Use Screen Time on your iPhone, iPad, or iPod touch - Apple Support
If your device is updated and you're following the correct steps, but your settings still aren't saving, reaching out to Apple Support directly is the next best step. They're better equipped to take a closer look at the issue and provide some additional guidance. This link will help you get started: Contact - Official Apple Support
Take care.