If the difference is exactly one hour, then the problem may be that you're using a date file for the wrong time zone, or one that for some reason doesn't properly manage change between standard time and daylight savings time. Check with your OS vendor to be sure you've got the most recent time zone files. This page (linuxselfhelp.com) though for a very old version of Linux, probably has some helpful information. You'll also want to be sure you're running a daemon (service) to update the time automatically. On my CentOs servers I add and configure the ntp rpm using yum.