First of all, you want to start with pears that aren't yet ripe. Ripe pears will fall apart too easily! The pears should be poached for around 15-20 minutes, the exact amount of time will depend on how big your pears are. But 15 minutes is a good marker, and from then you can test the pears by inserting a knife. They are done when it is easy to insert the knife, but the pear doesn't break easily.