We created the test application mentioned above, however the issue still exists there as well.
OS version - tvOS 17.6
Scenario
Open the application and click the "Save Date & Time to Keychain" button to save the current date and time to the Keychain.
Wait for 5 to 20 seconds after saving the date and time.
Reboot or unplug the Apple TV.
Plug the Apple TV back in and open the application again.
Observation
Upon reopening, the application retrieves the previous date and time value instead of the one recently saved to the Keychain.
Please find the Test application
[https://drive.google.com/file/d/17cgqZ0bSJQia5L-o5o6Cw2ZC2ekn4reo/view?usp=drive_link)