Solved (or almost)?
I’ve just updated (16.10.0) and had a nice surprise! After turning off and on again, without wifi, it took less than 5 seconds to update the clock. I saw the wrong time for some seconds, got an error message from a calendar or Whatsapp (can’t remember), but the clock instantly changed!
Can you confirm that it works on your phones?
If so, thank you FP to have fixed it, it’s a very good surprise. You could have communicated earlier that you were actively working on that, so we would have been more patient at the end, but the result is a good surprise.