Had some minor drama with the core switch clock being out by well over an hour. Not causing any issue except frustration when viewing logs and trying to compare timestamps across devices.

All the network devices get their time sync from the wan router (which in turn contacts our ntp server for its time).

To fix it up – remove all the ntp related statements from the cisco 6509, then manually set the clock to within 5 mins of the actual time as reported by the ntp server, then re-apply the ‘ntp server’ statement(s). After a short while the clock will re-sync correctly with the ntp server specified.

Never apply the ‘ntp clock-period’ statement – this is done by the device itself. I think someone manually applied this and that was why the time started to get way out.
ie. Make sure you never copy the ‘ntp clock-period’ statement from one device to another. The clock-period is set by NTP; to regulate the internal clock on the device. This is the number of ticks in one second. Therefore, NTP doesn’t change the time of the switch, it adjusts the clock-period so that the system clock is synchronized with the ntp server.