I got a boy from shettles on the day before o day.
I got boy/girl twins from 0+12, so it was 50/50 for me. I know it was also for sure at least 12 hours after o.
I went with Shettles personally, but I really don't believe timing is the key factor, more environment. I do understand the desire of wanting to try everything to get that girl though! For some reason, as I have been on these boards (gd boards) for years, that Shettles works if its a 2-3 day cut off, but I feel like the long cut offs result in boys more. 0+12 seems to work well for most, but it was only 50/50 for me so I figured I should try a 2-3 day cut off this time around....but that was just my thoughts for me. I do realize there are a lot of shettles opposites, but it did work for my ds1. Good luck!!!