I thought it was 72 hours...

According to FF (Fertility Friend)

How long can sperm survive in fertile cervical fluid?
The longest that sperm can survive in fertile (eggwhite) cervical fluid is five days. All pregnancies can be attributed to intercourse that takes place within the five days before ovulation and the day of ovulation.

Sperm, however, do not typically survive for five days, even in fertile cervical fluid. A life span of 2-3 days is much more typical for sperm, even in fertile cervical fluid- less if there is no fertile cervical fluid.