Similar problem here on 5.0.18 NE on Ubuntu 8-64bit.

Zimbra logs are one hour behind, the time on the Server Status 'updated' time is correct, but the services times are one hour ahead.

zmprov gc default | grep zimbraPrefTimeZoneId
zimbraPrefTimeZoneId: (GMT-08.00) Pacific Time (US & Canada)

date shows:
Tue Aug 11 10:56:15 PDT 2009

Times in the web client appear correct.