Heat Setting For Extension Springs

Hello Everyone,

I am doing research on the heat setting process for small extension springs, in aviation applications. The material is 17-7Ph. So far I have not been able to find much online. I am under the impression that it calls out for 400 Degrees (F) for 5 Hours, I would like to confirm this. The question I have is; Why the exact temperature and time? Is this an industry standard? If so, where do I find the specs?

Thank you,
Brandon F.