Managing NTP services on a MAAS node via charms is currently not really possible.
If MAAS is deployed from a deb package, the NTP charm and MAAS itself will fight over the control of
/etc/chrony/chrony.conf; if MAAS is deployed via the snap the situation will be even worse, as a second chrony binary is bundled in the snap, which will lead to unpredictable results in conjunction to the chrony deb the charm will install and configure.
It would be very useful if there was a way to configure MAAS to not handle NTP services at all. At that point the NTP charm could be made MAAS-aware and have it automate taking over NTP managing duties.