Here are a few things I like to do depending on your engine combo. When cranking the engine to achieve oil pressure you need to first prime the oil pump (assuming you have a full flowed engine), have a friend crank the engine till you have oil coming out of the pump, then re-connect the oil line, then crank the engine till the oil light goes out and you have a reading on your oil pressure gauge. (if you are using one) Depending on what engine you just built you I don't think you need to run the engine for 15-20 min. I think 2 5min intervals @ 2500 rpms would be sufficient. Then let the engine cool, change the oil, and re-torque the heads.