Tops of the Flowers began to darken, today is a good temperature 26-27 and humidity 40-50%, solution as instructions

so you applied a foliar spray? That probably caused it. A foliar spray for the sake of doing it is not a good idea. It has little benefit and adds needless risk like singing a pistil. It mostly just makes people feel like they are adding value, but nothing to back it up. In response to a specific problem it is fine, but only some nute molecules can traverse the stomata. Otherwise you are just creating a layer of dried up nutes on the tops of your leaves and flowers for no reason. That can be a disease vector and just being wet consistently is too. Asking for WPM... Excess wind can make pistils die early, too. Pollination can cause pistils to die earlly, so inspect for those just to be sure. Too much light can singe them, not likely here as it looks different. Either case, you plants look healthy. Stop foliar spraying them when there is no direct need. Especially with flower developing. Roots evolved to handle intake of nutes. LEaves are for photosynthesis, storage and transpiration. They've got enough on their plates. Definitely don't want to fuck with transpiration. that will fuck with co2 intake which is the limiting factor in most gardens.

I think you're overthinking things. Lookin good to me.

its not really a problem some strains will do this I don't think its anything you have done as the plant looks really healthy I would not worry about it buddy keep doing what your doing :) and you'll be fine :)