HELP shettles method! Trying to select gender

So I’ve been reading that there’s “methods” as to conceiving your child’s gender. like the shettles method that has a 75 percent success rate. Girl producing sperm (X-sperm) move slower but are more resilient and live longer than male-producing sperm (Y-sperm), which are faster but have shorter life spans. So if you want a girl, you should have sex two to four days before you ovulate — that way the X-sperm will be the only sperm alive and waiting around in your fallopian tubes by the time your egg drops in a few days later. If you want a boy, on the other hand, you should have sex as close as possible to ovulation — since the speedy Y-sperm will be more likely to get to the egg first. So my question is, can any of you back this up? I’m trying for a girl, so has anyone had sex 2-4 days before you ovulated & ended up being pregnant with a girl??