Pistils won't tell you when your plant is ready, you need to look at trichomes. Some plants have mostly white pistils when finished some red some orange some pink etc... But all will start with clear trichomes and progress to cloudy and then amber. Cloudy trichomes have the most THC and when you see amber that means THC is being degraded to CBN, CBD may also be more present resulting in a more couch lock high as opposed to a more uplifted feeling. Though that factor is also very strain dependent, it can just be enhanced by timing your harvest. In the end, what kind of smoke do you want? Full potency? Go will almost all cloudy with a few amber. More couch lock effect? Let more and more trichomes go amber. It's up to you, but as they go amber, you start losing THC.