Is 7 weeks plenty? Many growers go by 6 weeks vegging...
How long you veg is totally up to you. Some growers run 12/12 from seed. However unless your plant has reached its genetic maturity point it won't start flowering until it does. The plant biologically has to transition from veg to flower, and that can take anywhere from a few days to a few weeks depending on genetics and environment.
As for longer nights creating shorter flowering times, I can't say from a scientific point of view. I personally have tried a variety of different indoor light times over the years. I usually ran at 13 dark and 11 light because it saved a little electric on my 1kwatt flowering light and I didn't feel like I saw much difference from playing with the timer.
What I can say is that thinking about "harvesting as early as possible" before your plant has even began to flower is the wrong approach! Growing cannabis takes patients, and if you don't have the time or have the patients then you will struggle to grow anything quality.
Ak-47 is a sativa dominant hybrid, which means it has potential to take as long as it wants lol. Not really, but I 100% wouldn't believe the breeder claiming it's an 8-9 weeks strain, at least not 8-9 weeks from the flip. So be prepared to have this plant still growing 10-11 weeks from now if you just flipped your lights. Plants don't grow by calendars though, so don't worry about how many weeks its been or carefully counting the days. Just keep the plant healthy and wait until it shows you the signs it is actually done and ripe!
