Why is that there is no firm answer on when implantation occurs? ive heard as early as 4 days - and then no sooner than 7 days. seems like no one agrees on timing?

there is no exact time due to the variability. Good Luck

Most women ultimately have regular menstrual cycles, with ovulation occurring 12-14 days prior to the onset of each period. Implantaton of a fertilized ovum can occur anywhere from 6-9 days following fertilization, If coitus occurs at the time of ovulation, pregnancy is likely. Implantation is of lesser importance. If contraception is desired, see a trusted ob-gyn for discussion of options.