How often is sex necessary in order to conceive? daily sex or less in the ovulation days?

If you get lucky: Once is plenty. Most people try abit more to cover their bets. I recommend every other day around ovulation but every day is okay too. More than once a day is unnecessary and probably counterproductive.

Sex: One time is all thats necessary with some couples.

Just one time: If you are sure when you are going to ovulate, withholding sex for a couple of days before may increase sperm count and chance of conception.