You can use the Format Settings page to define custom formats for date fields.
- Enter a valid date format string to Date Format field to change the output format for "Date" type custom fields and DueDate system field.
- Enter a valid datetime format string to DateTime Format field to change the output format for "DateTime" type custom fields and Created, Updated, Resolved system fields.
- If no format string is given for one or both of the settings, the default JIRA date and datetime formats will be used. JIRA default format settings can be displayed and changed from "Look & Feel" JIRA administration page.
- The given formats are used for both on screen reporting and file exports.
Excel displays any recognised date value in the format Excel is set to use so even if you are using a custom date/datetime format, XLS/XLSX files will display them in Excel date format (if recognised as a date) or will display them as text (if not recognised as a date)