From the comments in the OP's blog by pilots, it seems to be common practice during pilot rotation (especially on the 764 given the remote lav location) is for a the first pilot to lock the lav, so the 2nd pilot has expedited access, and the continues for other pilots until the rotation is completed. It was stated this should be no more than 15-20 minutes. So this is a third mode, temporary blocked periods. I report here to add to the discussion and not to justify or condemn.

The original report was the observed closure was long and the reason given was not for rotation. But I am struggling to understand if this was a rogue situation or ordinary practice as my experience with 764s is very minimal.