From UFStarfleet Wiki
How to make the forum display Stardates instead of standard dates
1. Click on the PROFILE menu at the top of the forum page.
2. Click on the "Look and Layout Preferences" on the menu to the left of the page.
3. Copy and paste the following code into the "Time Format:" field -- %y%m%d.%H%M
4. Click the "Change Profile" button at the bottom right of the dialog.
5. Smile in smug satisfaction that you are geekishly cool!!