The problem with upgrading a cabin is not so much the fact it may take a few weeks but tha airline is not able to take an aircraft completely out of service for the work for that time, eg QF need at the moment every aircraft they can get there hands on.
If they have recently had delivery of a new plane and no new routes of flights it should be easy to do.
QF plan to have re-fitted a lot of the 744 fleet with premium economy and the new fabics etc by end of 2008. SO it must be able to be done.
E