They mention it, but Chrony is really amazing as a time sync solution for most environments. I've used most open source (and some proprietary) implementations of NTP and PTP over the years. Chrony is more reliable, simpler to configure, and better documented than all of them.
These days, I would always choose to use Chrony when possible.
Quoting the Chrony FAQ [1]:
> When combined with local hardware timestamping, good network switches, and even shorter polling intervals, a sub-microsecond accuracy and stability of a few tens of nanoseconds might be possible.
This is a level of accuracy many people think is only achievable using PTP, but Chrony can do it using NTP. Not that most people need this level of accuracy, but some do, and it's just plain cool.
Once you set up time sync, the next step is to make sure you have sufficient monitoring in place, so that you can stop worrying about all the subtle issues caused by out of sync systems.