This can occur from one of two reasons:
Timestamps shown in the JIRA UI don't match the users' timezone but that of the server location. The timezone used is a JVM system property which defaults - unless specified - to that of the hosting operating system
It is not possible to localize the timezone on a per-user basis. It is possible to change the JVM timezone by setting the following JVM command line property:
-Duser.timezone=<TZ>. Possible values are in the zoneinfo format (please see this list of zoneinfo time zones).
To set a command line option, see Setting properties and options on startup.
JIRA's date/time may not have been updated after day light savings has taken affect - this is generally an issue with older versions of JAVA.
Upgrading JVM to the latest version will solve the problem. Please download the latest version from java.sun.com.
For further reference, see the following document: