it may or may not be unusual. If the pistils are only turning color early in specific, isolated locations, then you can probably assume you are causing it. Is a fan directly pointed at those colas? Is it only the top colas in the most intense light directly under any concentration of diodes? Did you spray something on your plants? Should cover most of the bases, but i'm sure there's other things you could do to cause this, too.
Your temperature range definitely won't cause this.
If it is happening all over and fairly evenly, then it's just maturing faster than a typical plant.
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Call me "mean": I want to see a plant that sheds its stigmata. I've yet to ever see that occur. Do you have to sweep up mid-to-late flower? Probably caused by some sort of gimmicky foliar spray promising the world?