It depends on where you are located and what the temperatures are like. Not sure about bachelor buttons -- I think they are started earliest, it might be late for sunflowers if dog days of summer are already here, but morning glories shouldn't be an issue.
It will also depend on the opposite end -- when does the weather get cold/ first frost arrive and how long it takes for the flowers to mature and bloom -- what variety are you growing? Sunflowers in particular have wide variety.
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