When I was growing up, the pipe smokers I knew (father, uncle, grandfather, etc.), usually owned only 3-4 pipes and smoked them constantly. As a rule, they would smoke a pipe several times a day and then let it rest for 2 or 3 days, rotating among their modest collection. They did clean them regularly and well. I never saw a pipe burn out, go sour, break, or in any way suffer from this treatment.
Some guys will say to own a pipe for each day of the week, smoking each several times and then putting it aside for the next week. Others say to let it rest for a number of days equal to the number of bowls smoked. Some say to smoke a briar only once before letting it rest for several days.
Know what I think? There is no right answer. None at all.
The one thing I claim to know, factually, is that our briars are a lot tougher than some guys believe. They are pieces of wood, not high-performance jet aircraft. They are sturdy, reliable, and can most certainly put up with being smoked more than once a day before being set aside for a fortnight or whatever. Will a pipe deliver it's absolute BEST, crispest, freshest smoke if you overdo it? Of course it won't. But it's not going to keel over and go to Briar Heaven, either.
Personally. I often smoke a single pipe multiple times a day (4-6) and then let it rest for a week or so. Sometimes I've smoked the same pipe a half dozen times a day for multiple consecutive days. Sometimes I smoke only a single bowl before putting it back (I've learned some briars are better than others). But this doesn't have very much to do with me worrying about the health of briars. I do this because I dedicate briars to certain blends/genres, so if I want to smoke a wide variety of different tobaccos in a day I have to rotate through my pipes quickly. In any case, I've never had briar burn out, go sour, or anything like that.
My advice? Don't worry about smoking your briars too much. They'll be okay. Just make sure to clean them thoroughly after a day's hard use, and make sure you have enough of a rotation to give them at least 2-3 days' rest. Otherwise, forget about it and just enjoy smoking.