As all of you know, there are two choices for timing when swaying for a girl, although some couples do choose just to TTC during ovulation and not worry about timing. If you do choose to adjust timing to sway for a girl, you can choose between the CO method and O+12.
One bit of new information I have learned, is that against popular belief, sperm actually DON'T live at different rates or swim faster than the other, but do indeed, move differently. Male sperm swim straight, while female sperm zig zag in their movements. There is also evidence that male sperm weigh more than female sperm, due to carrying more DNA. This is why O+12 is said to be the better of the two choices and has the best success rate.
With CO (cut off), you want to TTC 2-5 days prior to ovulation. Sperm can't live longer than 5 days. 3 days prior to ovulation has been shown to have the best success. With this method, you must keep your pH low all the way through ovulation, which means the 2-5 days before ovulation, you have to be checking your pH on a regular basis and continuing the diet and douching regularly to keep pH at 4-4.5. MANY women end up with opposites with this method. The plus to this method, is that it is easier to achieve pregnancy and isn't as hard to hit timing of possible conception.
O+12 has a much better success rate than CO for two main reasons. One is that with this method, you're only introducing sperm into your body for a short amount of time, which means you only have to monitor and adjust pH for a short amount of time. With O+12, you want to watch for signs of ovulation, meaning that your cervix will be slightly open and you will have a lot of EWCM. Your cervix will also feel soft like your lips. AFTER ovulation has taken place, and your cervix closes, your EWCM dries up and your cervix feels like the tip of your nose instead of soft like your lips, you are at O+12. That is when you want to begin your attempt. You usually have about 20 hours to BD after you have confirmed that ovulation has taken place (the egg lives for about 24 hours total). Then you only have to keep your pH low for 24 hours. Also (this is the MAIN reason that O+12 works so well), after you ovulate, your body NATURALLY becomes girl friendly, because it is flooded with the release of female hormones (Progesterone and Estrogen). The downside to this method, is that it can be hard to pin point that perfect O+12 time, and sometimes women end up getting too close to ovulation, which is prime boy territory. Sometimes women can also wait TOO long and miss it altogether and not conceive because they egg is already dead. O+12 can occur at any time of the day, which means it can also happen in the middle of the night! You need to be checking your cervix and CM around the clock, even through the night. Some women even set an alarm throughout the entire night to get up and check. If ovulation does take place in the middle of the night, you certainly can BD right then and there, or wait until morning, since you typically do have some time before the egg dies.
Based on this information, it is up to each individual to choose the method they feel is best for them. Good luck to all!
If you have any questions, feel free to ask.