Actually, physically it is impossible.. if her bleed begins five hours after intercourse that means that her body has shed the uterine lining--leaving nothing for the embryo to attach to.
Also, if she did ovulate late then the progesterone would prolong her cycle from the point of ovulation- which would mean that she wouldn't bleed five hours from that point.
In terms of semen, yes it can survive for 72 hours BUT that is only if there is fertile cervical mucus present- which is only during the three (on average) days prior to ovulation and maybe a couple days after- the rest of the cycle the enviroment in the vaginal canal is too acidic to sustain semen for more than a few hours.
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