Some others have looked at being density to determine when to start using the beans and which grinder setting to use. I wrote my article reviewing the work that’s out there. I haven’t collected specific data, but I think being density is a good starting point, probably better than hardness because it’s hard to measure hardness of roasted beans because they’re so brittle.

https://towardsdatascience.com/determining-peak-flavor-of-coffee-using-bean-density-853404db300a