They are, but we use a program for Windows called ChronosXP that keeps track of them for us, if that is what you mean.
Other than that, hours are necessary when starting specific workings, things like Void Courses of the Moon, starting squares on their respective planetary hours, or choosing hours based on the goal (for example money spells are usually started on hours of the Sun or Jupiter). If you don't find specific information on the JoS try searching the forums, and if there's no luck there either, you can always ask more specifically. Hope this helps.