This PI3 is shockingly badly off with the clock. I checked just now, 10 hours later. And it is another 20 seconds out. Thanks to the command supplied I can now request a sync… but that fails on the first 10 attempts. Which kinda matches the earlier situation where it only tried 9 times before giving up.
The funny part of the above image is the clock was 20 seconds out at the start… and then the fix took 20 seconds to complete. So it looks like time stood still while the clock corrected 
What makes me curious are the 11 attempts required to sync. This explains why that initial attempt of changing the NTP server fails as it is just too slow to respond for ten tries.
Don’t know why it is so slow… a second attempt gets a reply on the first try.
Next question to self - do I swap to a PI4, which would mean scrapping the PI3? Or do I get it a RTC chip? As it stands this thing is loosing two seconds an hour.