Some research say a day before ur ovulation while some say on ur ovulation day. The reason is Y chromosomes which produces a boy is faster but dies sooner than X chromosomes, if released 3 days before ovulation, it dies after 24hrs while X which produces a girl can live for 72hrs. If released on ovulation day, Y Chromosomes get there first and fertilization takes place, a boy will he conceived. But first, u av to be sure of ur ovulation period. Ive seen it work for some ppl but note that above all, God is d giver of Babies. All d best!