Visited interior of 4 villas in one day on Sunday in November 2019. This could only be done with advance planning, pre-booking and using rented car as follows.

Villa di Poggio a Caiano – this one has regular opening hours, it opens at 08:30 and there is free accompanied tour each hour. Villa has extraordinary interior, including original frescos by Andrea del Sarto in the central hall on the first floor. There is little to add to the previous reviews. 
 
Villa Artiminio (Ferdinanda) – this is private property now, which includes winery, hotel and restaurant. There are occasionally guided visits and we booked one in advance for 11:30 for 12 euro. Villas was built in 1596 as a hunting lodge. It has a lot of chimneys on the roof in order to heat the villa during winter times and is sometimes called villa of hundred chimneys. Unfortunately, in 1950th all the interior, furniture and decorations were sold by the private owner at that time through auctions and only certain pieces were purchased back afterwards. However, there are a number of survived beautiful frescos by Passignano, including entrance hall (pictured), internal chapel and small bathroom. External staircase was only completed in 1930 using original designs of the architect Buontalenti. There is also storage of wine on the ground floor and even secret underground tunnel to be used by the Medicis in case of danger. After the tour we acquired excellent Grumarello and Rugiolino wine from the local winery.
 
Villa della Petraia – this also has free accompanied entrance each hour, we entered at 14:30 with another couple and very grouchy type who was opening the rooms. Villa has good views over Florence and is one of the best medicean villas. It has amazing fully frescoed grand court. Also, 14 surviving paintings of Medici villas by Giusto Utens were moved here in 2014 after the Unesco inscription.
 
Villa La Magia – this could be visited with guided tour for 8 euro each Sunday at 16:00, but you have to reserve this tour by e-mail in advance. We were only four people for the tour; the guide was extremely knowledgeable and informative. This is the only villa of all, which is not really Medicean, it was constructed by the local Panciatichi family in the fourteenth century and was only afterwards purchased and owned by the Medici the 16th century as convenient stopover point between Pistoia and Florence. The last private owner, the Countess Marcella Pagnani Amati Cellesi, lived in the Villa alone until 2002. Two years earlier the ownership was passed to the local municipality of Quarrata, which has been painstakingly restoring step-by-step the villa. There are several beautiful frescos dated 17th century. A number of rooms lack decoration and still awaits restoration works. There is also a bid garden around the villa with contemporary art installations and a good view over surrounding hills.