Since sperm live for about 48 hours after ejaculation, and the ovum for only 24 hours after ovulation, intercourse can occur one day after ovulation for fertilization to occur.
As the speaker explains, sperm cells can live for 48 hours after ejaculation, and in fact, depending on location (for example the inside of the woman's vagina) they can survive for a longer time, even 5 days. Knowing this, there's a chance that if these cells are present in the vagina a few days before ovulation, fertilization can occur. On the other hand, if ejaculation takes place near or inside the vagina within these 48 hours, the sperm cells can also reach the ovum before it dies.
