If you do need sub-ms accurate time keeping, then "just" running ntpd is not enough. You need to have a low-jitter connection to at least one stratum 1 server (

If you do need sub-ms accurate time keeping, then "just" running ntpd is not enough. You need to have a low-jitter connection to at least one stratum 1 server (if you don't know you have one, you don't), or a local clock. Otherwise, ntp doesn't give you more precision over openntpd -- only faster convergence after you've lost contact with servers for a few days. If you don't know _exactly_ why you need ntpd, the default should be openntpd.