Different teas and different palates = very different brewing times. For one of my favorite shu (ripe) puerhs, I tossed a chunk into a thermos of hot water today and ran off to a meeting, and three hours later, the end of the thermos was still tasty. For a favorite sheng (raw) puerh, I pour hot water into and out of the teapot as fast as I can 5-10 times, drinking each 'flash' infusion quickly before it can start to turn a little bitter, and gradually increase the steep time to 5, 10, 20, 30, 60, 90 seconds etc.
How do you know what to do with the puerh in front of you?
Try it. Pick a time, and try it. If the tea is undrinkably bitter--dilute it until you like it, and then make the next infusion proportionately shorter: e.g., if you have to dilute the tea three fold to make your 1 minute-steeped tea taste good, then steep it 20 seconds for the next time. And keep steeping at 20 seconds until it's weaker than you like, and then extend. If the tea is too weak, steep longer next time.
Just play with it, and if you are so inclined, taking some notes on tea quantities and steeping times may help shorten your learning curve until you start to have an intuitive feel for what you'll like.
I'm only about 4 years into my appreciation of puerh, and I get more infusions right the first time than not, but still have some that.....um....need a lot of help!