How long does it take to conceive right after intercourse?

Depends. It depends on where you are in your cycle. Ovulation is 14 days before your next menstrual bleed. That is the peak time to achieve a pregnancy. The time it takes for the sperm to reach the egg varies depending on where the egg is at the time. It is usually a few hours..
Within 72 hours. Sperm can survive in your body up to 72 hours, so that would be the quickest time interval in which conception can occur. This assumes you are ovulating and had had intercourse at the right time.