(internet connected systems only)
While this probably should be done by your OS, from cron
Here is a script to sync your time with NTP.
Give it a name (synctime.sh) , Apply ownership
Give it a command in rpt.conf, Run that command from the macro/sched late at night.
#!/bin/bash
/usr/sbin/ntpdate pool.ntp.org > /etc/asterisk/log/timelog.txt
Will also create a log file if you need to check that it has been running correctly.
If not needed, delete all after and including ">"
Hopefully these are more of a example of how to do other things for those that are learning.