Can paternity be determine and a correct conception date is sex between 2 different men are 5/6 days apart?

Difficult to do: It is difficult to get conception dates accurate within only 5-6 days. Dates are usually accurate within 2 wks with good ultrasound and menstrual history. (Women who have irregular menses are a little more difficult to get accurate dates). In regards to paternity testing, you would need to get a DNA sample of both men and compare it to the DNA of the baby.