I feel very strongly that most of the effect from the weed is strain based, and not based on when you harvest. If you harvest early, you get less high, and it doesn't last as long. If you let it ripen properly then you get much more high, and it lasts much longer.
If you want an upbeat and speedy high, grow a strain that is known for providing that like Cinderella 99. I've grown strains that were very couchlock, and others that were not.
I've never grown a plant that was REALLY finished at under 8 weeks of actual flower time. Actual flower time begins when the plant starts forming flowers, not at 12/12 flip. Many people try to count the transition period as part of the flowering time which leads them to believe that the plants have been flowering longer then they actually have.
I don't count flower time, and havn't in years, its pointless. The plants will be done whenever they are done.