Hi, I'd like to report on my Chatuchuck trip.
I went there Dec. 31st which was a holiday in Thailand, Thursday. Arrived around 6am by Taxi from the hotel.
When we arrived, was happy to see that there are lots of plants out and store owners already cleaning and greeting us. But no CPs. We walked around a bit, then I saw some Ventratas, never bothered to ask price, then saw one that had Ceph, and then in the corner (near Soi 34) where the Train station is located, there was one shop that had lots of Nepenthes, some pings and come droseras and Cephs, but no shop owner. We went around a second time, and saw a store selling Mirabilis for 50 baht, no thanks. It was by this time around 7am, and when we got to the corner store that had lots of CPs, the shop owner was still not there, so went back to the one that had ceph, and saw he had 2 neps too. Asked the price, and the species, he said one was N. x Viking and N. Thorellii, how much? 500 baht, no thanks. The ceph was going or 850Baht.
We left at around 730am, with no other stores open except the plant shops and some plant shops are still without their owners, maybe the owner went for breakfast or something. We couldn't stay longer because we had to go back to hotel to get ready for a tour to the Safari/zoo.
I noticed that the plants being sold were mostly not housed in proper shops, but in the "road" or walk area surrounding the actual stores. So yeah most probably they are temporary, in the official map of Chatuchak, there is a plant section but it is not as big as if you go wed. or thurs. maybe... I am not sure what time the whole area opens during weedays though, but as I said when I was there at 730am, most of the actual shops were still closed and those with plants outside might still have their shop owners having breakfast or something.
http://www.chatuchak.org/map.html