This issue may be more a connman one than systemd
but I put it here since this bugtracker has more visibility.
I though it was a good idea to collect feedback here and
have no objection in marking it invalid or closed.
I Will also cross-post it to connman tracker too 
https://01.org/connman 

So here it goes, on the distro I am working on
It was wanted to avoid launching connman-ntp service  
(especially if NTP is not wanted by user), 
and then use it as a "onshot" service 
(see attached file : connman-ntp.service).

But relying on the enabled status of NTP unit providers is not enough,
since those could be installed as "static services"
so we can not rely on this, and the internal state should be queried.

So I had to make systemd query the real connman state, 
and then introduce a reference to connman into systemd ;(

I can understand this won't be merged into systemd and 
kept agnostic to implementations of NTP services.

So the question is :
Can you suggest a proper/better way to interact with connman-ntp ?
Or what are the plans to have a generic behaviour on NTP ?

I have checked TODO file and this documentation :
http://www.freedesktop.org/wiki/Software/systemd/timedated/

Anyway let me share that patch which basically do a dbus call
and update accordingly when in given configuration.
    
This is fixing issues like unpreserved/inconsistent states
between freedesktop and connman (specially after rebooting).