Hi
yes indeed you can configure any device to get time from an public time server,but the downside of this method is that all these servers do not commit to provide time service other than on a volunteer basis and with no guarantee of accuracy or availability,
here is a list
http://ntp.isc.org/bin/view/Servers/NTPPoolServers.
from a security perspective i would like to mention that is not a good way to go with, because imagine a situation in whitch you are using digital certificates to authenticate users, you have to know that a correct time for digitale certificates is crucial if you are using a server from internet attackers can fake the time in manner to make these certificates expired and that will lead to the failure of every connection if you want it s a kind of DOS denial of service, the same things those attackers can fake the time in your syslog so that you cannot know the exact time of each behavior of you network so try to not use that and go with a local NTP especialy version 3 that is built with security in mind.
HTH
please do rate if does clarify
