there is alot of difference with changing parts only or redesigning the part of the board where a new part will be. if the parts are almost identical in everyway, its a matter of just loading the component reel on the feeder ,reprogramming the fuji or DEK then away you go . however if the supplier sold the new components in tubes then its more time consuming, even morseo if the part is not the same dimensionally. this means board design changes, solder paste screens need to be made, gerber files to be modified and in some cases completely new pcbs made,a different feeder needs to be jigged up and then a full QA check along with new functional testing. we do part changes often with products 100 times more complex but speed comes down to how big the work force is and how much experience they have. we do take alot for granted and its not like replacing a light bulb. i too am awaiting my mmm, unfortunately i know what goes on and its not a weekend thing.