It's all very well doing the rapid change when all is going smoothly and no defects are found etc..
The management always use this as a benchmark though and want it every time afterwards.
I'd rather do a quality, safe job than try and get in the Guiness book of records (or Aviation Disaster Yearbook!).
BA apparently did a 74 RB211 in 4.5 hours recently, hope they're ready for the abuse when the next one takes double the time.