I assume you are trying OS version 16.10 (not 16.0.10). The feature you describe was added in 16.08.0002:
After the switch is power-cycled or rebooted, the switch system clock is now set to the last known good time rather than being reset to the factory default.
It's not fully clear to me what the last known good time would be, but I'd assume that is every time the NTP synchonises time, and from your experience, I understand it is when you manually set the clock.
If it is about getting NTP to sync quickly, have you configured the iburst command on your ntp?
ntp server 192.168.2.1 iburst
That will very quickly sync the time to that server on initial contact, even if that server is way off the local clock.
If you have ntp enabled and synced and find that after a restart of the switch the time goes back to your manual time set rather than a time set by NTP, please open a support case as that behavior does not match the description.