How long will my plant take to get to 1 foot?

That's the size I want it, for personal use. I will never sell it. o:
Since this is my first grow, I figured I would go with something not to challenging and only let it grow to 1 foot, then flower it.
My plant is 3 days as a sproutling, and 3 inches tall. Plant number two is day one as a sproutling, maybe an inch tall.
How long should I let it flower for better quality buds?
 
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