Generally, restaurants are open from noon to about 2 and from 7:30 or 8 to 10 or 10:30. It's best to make reservations, particularly in summer, although the reviews only state when reservations are absolutely essential. If you want no-smoking seating, make this clear; the mandatory no-smoking area is sometimes limited to a very few tables. Brasseries have longer hours and often serve all day and late into the evening; some are open 24 hours.
Assume a restaurant is open every day, unless otherwise indicated. Surprisingly, many prestigious restaurants close on Saturday as well as Sunday. July and August are the most common months for annual closings, although Paris in August is no longer the wasteland it once was. Places where a jacket and tie are de rigueur are noted. Otherwise, use common sense -- jeans and T-shirts are not suitable in Paris restaurants, nor are shorts or running clothes, except in the most casual bistros and cafés.