Answer: All of the buds on a flower should open at about the same time, within a day or so of each other. The entire flower shoud basically be open at once. Eventually they wilt at about the same time although a few that opened last will stay a little longer.
What you are describing sounds as though there is some sort of problem, possibly a fungal problem such as botrytis which can cause part of the flower to turn gray or brown or fail to open and tends to happen during wet weather or if the plants are constantly wet from overhead watering. There is an extreme photo of it here:
When you deadhead or remove the faded flower, cut at the bottom of the wiry stem just above the first leaf. Take off the whole flower at once. I hope this helps!
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