It depends on what kind of high you want.
If you harvest early when there are maybe 10-20% brown hairs, you get a more actieve high.
when the hairs are like 80% brown you get a nice balanced high and when they are 100% brown and the buds are little overriped, you get a real strong sleepy high.
If you grow like a haze sativa you really want to get that early harvest to get that actieve high or it doesn't make any sence haha because most of the times
indicas are like the sleepy ones. But again you can harvest a indica earlyer as well to make sure you don't have that heavy sleepy high.
What you really should look at is at the THC, get yourself, if you dont have one yet, a microscope. When like most of the THC (Thricromes) are looking milky instead of crystal, your THC is ready.
if you have some brown thricromes don't worry but don't get to many of thoose, They will be more of thoose in time.
When not having a microscope, just wait until the hairs get like 80% brown :)
Goodluck :)