During my stay in Europe, I found out that shopping malls and shops were not open daily including supermarkets. It closed on weekends, and closed early on weekdays (I mean around 17.00). Besides, some shops closed during the days such as around 11.00 to 14.00.
At first I was upset because I always went to the shop and found out that it just closed a few minutes ago. Then, I learned and adjusted. Soon, I found out that I always had plans for buying fresh foods from supermarket every week because supermarkets closed on weekends.
In Bangkok, you do not have to worry about this. Generally shopping malls in Bangkok such as MBK Center, Siam Paragon, CentralWorld, Terminal21 are open daily from 10.00-22.00. They are open on weekends and also during the festivals. In my life I saw the shopping malls in Bangkok closed only once or twice. At that time, they closed because of the political situation; many protesters gathered in front of the malls.
Supermarket chains such as Tesco Lotus are also open daily, but a little bit longer like 8.00 to 23.00. 7-eleven convenient stores are open 24/7, and you can find them all over Bangkok. Independent markets and shops have their own opening hours, but they likely to open on weekends.
Hope this information helps.