It depends on how much you effort you put into your affirmations.  Studies have shown that with repetitive reconditioning you can create new neural pathways in about 28 days.

Years ago, NASA designed a fascinating experiment to test the psychological impact of special disorientation; NASA outfitted a group of astronaut candidates with convex goggles that flipped everything in 180 degrees vision of their field, so that the world they saw was completely reversed. The test subjects wore these glasses 24 hours a day, even while asleep. Then the scientists sat back to observe what happened.

At first, the extreme stress and concern were obvious, Upside_down_goggles,_инвертоскоп_(invertoscope)as reflected in the astronaut’s blood pressure and other vital sign. The astronauts gradually adapted to this new level of stress, but it still didn’t dissipate altogether. After all, their entire world was reversed. But 21 days after the experiment began, something amazing happened to one astronaut. His world turned right-side up again. The goggles hadn’t changed and he was still wearing them continuously, but now he was able to see everything normal around him. Then for the next several days, all the other astronauts followed suit.

What had happened? After 21 to 30 days of his constant stream of strange new input, the men’s brain had created enough new neural connections to completely rewire their brains, so that their visual and spatial perception worked at 180 degrees opposite from the way the brain normally works. In repeated trails, the researchers also discovered that if the goggles were removed during approximately this period of month, even for short times, the neural variation would not occur. In other words, it took about 21 to 30 days of uninterrupted, constant input of new perceptual (conscious) information for the subconscious brain to accept that it had to adjust to this new information and consider it as normal.