Yes it's true and yes it is very hard coded. Yes it uses standard port 123 UDP.
Jamf is the Apple Business Manager for iOS devices and there is no setting in there either. See https://www.jamf.com/jamf-nation/discussions/11772/ntp-server-for-ipads
Like the article says create an A record for time.apple.com and set the IP to your NTP server and that's it.
The current available public version is iOS 12.3, with iOS 13 due for release soon. iPod touch 4th generation can't update past iOS 6.1.6, and it is not possible to install iOS 9 on it.
iOS 6 is pretty ancient and not a lot of 3rd apps support it. There has been major design changes starting with iOS 7, and architectural enhancements in later versions of ...