If you are going to visit Bangkok, I am sure that Chatuchak Market must be one of your destinations. The market is famous for its size and the vast variety of goods.
For the best time to go to this market, first of all, you have to know that Chatuchak Market is a weekend market. The market is fully open only on Saturdays and Sundays. If you are a visitor who want to visit Chatuchak market for its unique experience, I recommend you to go there on weekend only. Well, if your time in Bangkok is on weekday, skip this market and fill your itinerary with somewhere else. The market is quiet on weekdays; only some parts of the market are open on weekdays such as plant section and aquarium section.
Chatuchak Market is open from 9.00 to 18.00. However, the best time to visit the market is in the morning and in the evening. As you may know, Bangkok is hot all year round. And, Chatuchak is an outdoor market. In the afternoon, you can expect intense heat and strong sunshine. I usually go there either 9.00-11.00 or 16.00-18.00 in order not to be melted in the market.
Recently some parts of the market have the air condition running, but only small parts. If you visit Chatuchak Market in the morning, I recommend you to have lunch at Or Tor Kor, the upscale fresh market. You can go there by MRT Subway. I like the food court there; it offers a vast variety of food and all I have tried are delicious. Then, if you still want to do some more shopping, I recommend you to take MRT Subway to Union Mall, an indoor shopping mall which is popular among locals.