It is more complex than expected.
In __connman_timeserver_get_all() connman is creating the NTP server (NTPS) list from
- explicit configured service NTPS (configured via "Edit" of the connection/service but not for DHCP)
- DHCP NTPS
- Gateway (if enabled, in LE not)
- Global NTPS (configured in LE Network tab)
- Fallback NTPS (of main.conf)
The first accessible NTPS is used.
After the fix mentioned in vpeter's gist this seem to be working as designed.
To configure your desired NTPS of 1. use
connmanctl config <service> --timeservers [NTPS1 [NPS2 ...]]
The service name list can be obtained by connmanctl services, the current service configuration is listed with connmanctl services <service>.
The UI of LE-Settings addon does not represent this behavior. The "Edit" option is listing the beginning of the complete NTPS list but store the values to connman's Timeservers.Configuration.
Consequently the save option is forbidden for a DHCP connection.