I am from india. since egg will be available for fertilization only up to 24 hours , chances of getting pregnant from sex 2 days(48 hours) after ovulation is zero? that is the logic. correct?

A released egg will be able to be fertilized for 24-48 hours, but sperm can remain viable for multiple days, so exposure to sperm even before release of the egg will extend the "fertile period" accordingly to five or six days. If ovulation times are regular and occur fourteen days prior to the next period, one can plan for conception by sexual exposure 3-4 d prior to ovulation and 2 d after.