[CentOS] Gradually adjust NTP sync over time?

[Sean Carolan]

> This is already how ntpd works.  When you first start the service
> (usually upon reboot), it will use 'ntpdate' to do a hard set of the
> clock, then ntpd picks up and adjusts the clock back and forth to keep
> it correct.

My understanding was that ntpd will use "slewing" for adjustments of
less than ~120ms or so, but for adjustments between 120ms and 17
minutes it will use "stepping" instead, making an abrupt and immediate
adjustment of the entire delta.

What I'm trying to avoid is abruptly resetting the clock from 12:06 to
12:05 all at once.  Instead we want to slowly turn the clock back that
one minute, but spread the changes across several hours or days.