it will depend. is your pipe new? is your pipe pre carbonized or naked? also depends on the tobac and how often you smoke your pipe. if your pipe is used or estsate, it should not take too long. hang in there. hope this helps.
As has been said, it really depends on so many factors there's no way to give you a definite answer. I've had pipes that broke in effortlessly and I have one pipe that was a real pain to break in. It tasted terrible for almost 20 bowls and took probably 50 bowls before it smoked well without giving me fits. It's now one of my best smokers. My advice is to just smoke it and don't worry too much about it. It will happen when it happens.
Depends on how often you smoke it. When I get a new pipe in, or when I restore an estate, I'll smoke the daylights out of it till I feel she's mine. Like breaking in a horse. Course I let er up for air once in a while, but I give it the good go through. At this point, about a week on, after say 20 smokes, why I'll have a nice cake forming. Then its just a matter of maintenance, and cake trimming if needed.
Course you can always buy a pre-smoked pipe. Talk about workplace smoke exposure! LOL.
When I get a new pipe I fill it to the top and smoke away. Most of my pipes take 15-20 bowls and then I feel it is fairly broken in. I like to smoke a new pipe every other day for those 15-20 bowls and by the time I am done the pipe will have a pretty nice cake developed. This method has worked well for me since I began breaking in new pipes 13 years ago. I figure I have broken in over 60 new pipes over the years and not a one has ever had a burn out or had any problem by me filling it to the top and smoking it. I also smoke a new pipe like any of my broken in pipes and never baby them. Granted I make sure not too over heat my pipe, but quality briar is a lot tougher than most people think.