Hongkees (the widely used and not negatively associated slang for Hong Kongnese) like flowers and the Flower Market (take the MTR to Prince Edward and use Exit B1) is also a popular tourist attraction. The market is open until around 7 PM daily.
This is one of the main roads where the flower shops are located. The area is not big, and once you found the first flower shop, navigation is easy, at least topologically. It can be quite crowded, because many locals and tourist will shop here. The prices at the flower market are significantly lower then in most flower shops, because they are buying here too ;-)