Originally Posted by
atomic sagebrush
No one really knows for sure and it's probable that it's different in every month for every fertilized eggo. Your lining, where the egg is fertilized, and how quickly it moves down the tube and implants, all affect odds of success. A fast moving egg fertilized a bit after O near the bottom of the Fallopian tube that has a nice lining to implant probably can make it in 7 days, whereas an egg that moves more slowly, is fertilized late, etc. may need more like 10+ days.
People have gotten pg from LPs of 7-8 days, while others with LP of 10 days have struggled. 12-14 is best, 10-12 is borderline, 7-10 is possible but not as likely.