This is a very basic operation on a Linux system, but I have to interact with it so rarely since I run either chronyd or ntpd on all of machines. Occasionally, I find a device that needs a helping hand.

On a device with a known good time (or approximate enough):

date +%s

This will get you the current unix timestamp. On the target system needing updating as root (replacing <unix timestamp> with the results from the last command):

date --set="@<unix timestamp>"
hwclock --systohc

Ensure both clocks are updated:

hwclock --show