Good question I have almost 82K on my car and I have adjusted regularly but I am not showing much wear on my brake shoes and I have not replaced shoes on a car since the 1980's. But then I think I only did that because I was bored or wanted to do maintenance on my car which at the time was a 1979 AMC Concord. I would just check them when you adjust them but you should be good up to 100K on them.
They are not difficult to check. Just need a T-30 torx fitting and a jack. I am surprised you have not adjusted yet. I would suggest adjusting and at that point you can see how good they are.The rear drum brake can't the inspect easily,