seat covers

An hour or two to get seats in & out, then an hour or two per seat to swap over covers. Guess you'd comfortably do the whole changeover in a day.
Not done ZS seats but on other cars I have done a lot of the cover is held in place with small copper rings (probably some proper upholstery term for these!), think you'd need some new ones of these and possibly some kind of special pliers to fit them. I got round it by using small cable ties - advantage is you can also fit a few then tighten them as needed to get the material nice and evenly taught.
Plenty of pics or drawings as you strip down is good idea and make sure you get the bit with "Airbag" on it in right place / right seat (it has weaker stitching to allow the airbag to burst out)
HTH