I think the recommended tire rotation time is 7500 miles...
If you look in the Maintenance forum, there is a sticky topic there about maintenance intervals and there should be a link to Nissan's site (which will show the recommended schedule).
You should also have a schedule in a book in your owners manual packet thingy.
I just did mine myself this morning. Have 8000 miles on mine. Only took about a half hour to do. TPMS worked fine after the change which was my only worry about doing it myself.