Thai business hours generally follow the 9 to 5 model, though the smaller the business, the more eclectic the hours. Nearly all businesses either close or slow to a halt during lunch hour—don't expect to accomplish anything important at this time. Many tourist businesses in the north and on the beaches and islands in the south often shut down outside the main tourist seasons of November through January and June through August.
Thai and foreign banks are open weekdays 8:30 to 3:30 (sometimes longer), except for public holidays. Most commercial concerns in Bangkok operate on a five-day week and are open 8 to 5. Government offices are generally open weekdays 8:30 to 4:30, with a noon to 1 lunch break. Generally speaking, avoid visiting any sort of office during the Thai lunch hour—or bring a book to pass the time.
Gas stations in Thailand are usually open at least 8 to 8 daily; many, particularly those on the highways, are open 24 hours a day. Twenty-four hour minimart-style gas stations are growing in popularity. Many also have fast-food restaurants and convenience stores.
Each museum keeps its own hours and may select a different day of the week to close (though it's usually Monday); it's best to call before visiting.
Temples are generally open to visitors from 7 or 8 in the morning to 5 or 6 pm, but in truth they don't really have set hours. If a compound has gates, they open at dawn to allow the monks to do their rounds. Outside of major tourist sights like Wat Po in Bangkok, few temples appear to have fixed closing times.
Most pharmacies are open daily 9 to 9. You'll find a few 24-hour pharmacies in tourist areas.
Most small stores are open daily 8 to 8, whereas department and chain stores are usually open from 10 until 10.