Ensure that all the host systems use the same relative time source, including the relevant localization offset. You can correlate the relative time source to an agreed-upon time standard such as Coordinated Universal Time (UTC).
You can easily track and correlate an intruder's actions when you review the relevant log files. Incorrect time settings can make it difficult to inspect and correlate log files to detect attacks, and can make auditing inaccurate. You can use at the least three NTP servers from outside time sources or configure a few local NTP servers on a trusted network that obtain their time from at least three outside time sources.