Wp Super Cache with Nginx - Timestamps differ

This is the test result from the admin page of Wp-Super-Cache.

Test your cached website by clicking the test button below.

Fetching http://domain.com/ to prime cache: OK

Fetching first copy of http://domain.com/: OK (1.html)

Fetching second copy of http://domain.com/: OK (2.html)

The pages do not match! Timestamps differ or were not found!

When I view source I do get a wp super cache stamp in the footer...

The trouble is everything is still running slow? and I am not sure how to correctly benchmark it.

Anyone got wp super cache working on nginx? thanks

Johnny