12/12 will be fine.

Never done the 48 hours of darkness so I can't say.

If you want to harvest in 6 weeks, instead of the avg. of say 8 you can. However, make sure you don't harvest just because 6 weeks is up. The trichs may not be ready and you will have harvested bud prematurely and the stone will be shitty and short.

To facilitate your expedited harvest date, you need to shorten the hours you have her in lite... 12 / 12 WILL NOT cut it...most likely.

Cut her down to 9 - 10 hours a day. That will force more rapid flowering and resin production but you will pay for it in yield or harvest quantity.

So take your pic....

More weed....shitty buzz
Less weed, better buzz....

If you choose the latter, keep the plant as dry as possible thru her 6 week flower. DRY...watering only in her "morning" cycle and do NOT water till she drips from the bottom. Just give her enuff to keep her from wilting.

Also do NOT do anything to raise the humidity of the air. Keep it as low as you can.

These steps will mimick the growth conditions they have in parts of the world where the most potent weed and by products like hash and oil grow naturally...the middle east, afghanistan. pakistan, etc...

With luck and care, you can have a small harvest of pungent smoke without sacrificing quality...just quantity.

HAPPY GROWING