Documentation for JIRA 5.1.x. Documentation for other versions of JIRA is available too.
The default time zone is set by your JIRA administrator (see Configuring JIRA Options), but you can personalise your JIRA account to use a time zone of your choice. This will affect all time-date fields throughout JIRA.
If the time zone specified in your JIRA user profile doesn't match the time zone of the computer you are working on, JIRA will prompt you to ask if you want to change the time zone setting in your JIRA user profile.
To choose a time zone: