I was getting this error in my log files:
dovecot: IMAP(user): Time just moved backwards by 1 seconds. I'll sleep now until we're back in present. http://wiki.dovecot.org/TimeMovedBackwards: 1 Time(s)
Looking at the website that was linked in the error message (very helpful), the solution was to edit /etc/ntp.conf and add the following:
# Added following to get rid of dovecot "Time moved backwards" error tinker step 0
Restart ntpd and after two days the error stopped showing up in my logs. Yay!