I like to spend a fair bit of time running an engine in on the test stand, first because I love running engines and like to learn what each engine needs to get one flick starts and second because even Jett say their engines need about 30 minutes to run in the conrod. I'm probably over cautious coming from a CL background when, if the engine happens to go lean in flight, you gotta wait until the tank runs dry . With ringed engines (as are almost all 4 strokes) I really take my time and give them at least an hour on the bench.