If you purchase a quality "no-retorque" gasket, then you do not need to do it 100 miles/100 kms after replacement. With cheap gasket you may want to do it anyways.

Either way, Nissan recommends an semi-annual re-torque:
Quote:


Tech: Head gasket

The most important things are:
* Clean the block face, head face and bolt holes thoroughly. The gasket may fail is this is not followed fastidiously
* Use a torque wrench, tighten in stages, and according to pattern

Most failure are due to not using a torque wrench or following the stages. A lot of owners just guess, and sometimes it works, but sometimes not.