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good question bt difficult to answer as it depends on the individual longevity of sperm, the internal metabolic capacity of sperm, the environment of the vagina (body temperature, ph levels, relative acidity), the presence of cervical mucus, the quality of cervical mucus, the ability of the sperm to get out of the vagina and into the womb, and the presence of sperm antagonists like immunity securing white-blood cells.
On average, we can expect sperm to survive just a day or two, and given more optimum conditions or luckier happenstance, a handful of days more.
Of course, with each passing day more and more sperm die and the odds of conceiving diminish
need not worry wait for your menses date if it get delay for 1 week you need to go for pregnancy
test and consult gynaecologist.