As Ben says, it depends on the individual and also how many bowls of tobacco you smoke daily.
If you have seven pipes and you smoke 2-3 bowls a day, for example, you can choose to, on one end of the scale, smoke your three bowls in one pipe, because it will be a week (plenty of time for the pipe to dry properly) before you pick up that pipe again. Or, still using the 3 bowls a day example, you can smoke a bowl in each of 3 separate pipes on the same day -- and still, your pipes will dry fine before you smoke them again.
See my math here? IMO (and I'm with Russ Ouelette on this) --in essence, a pipe should be allowed to rest and dry one day for each bowl you smoke in it.