No - there is an automatic floating rule named "let out anything from firewall host itself". That takes care of that. Generally you practically never need outbound rules on an interface.Do you see any blocked NTP packets in the firewall live view?
What do you have set in Services > Network Time > General > Interfaces?
Leave it at All (recommended) and try again, please.
What happens if you try to open a connection to the IPv6 server on port 123 with UDP with netcat or similar?
Please use "All (recommended)" and do not select any individual interfaces.