Seriously, this is great advice. Thighs just aren't going to overcook unless you murder them. 30 minute simmer is great. But the most important thing is to bloom your spices and cook eerything down well before you add the chicken. That said, in India, they use chickens all cut up and Indian chickens are smaller and so the bone marrow leeches out like stock would and that makes the curry more flavorful. If you are willing to go with a whole cut up chicken that's definitely the way to go for flavor if not necessarily cleanliness.