As you mind in using a stress test, I guess you're planning to overclock your CPU (obviously, its a k version). Normally, if you want to test the max. average temperature would be in 5-10 min. But if you got into unstable problems and don't know how to tune properly voltages, for a stable test it would be 3-5 min to make sure it is running steadily. Just be careful to not overvolt your cpu. You can always look out for any overclocking guide of a 4770k as it is a common processor.