Timing is more important for IUI than it is for intercourse. The reason is that, during intercourse, sperm travels through the cervical canal. There are glands and mucous in the cervix that sustains the sperm and acts as a reservoir that releases sperm into the uterus slowly over several days.
During anintrauterine insemination, the sperm are released into the uterus. The sperm do not remain viable for as long a period of time. Consequently, the sperm must be inseminated close to the time of ovulation.
One method to time an IUI is with an ovulation predictor kit. The kit measure a woman's LH surge. The surge peaks about 12-24 hours before the egg is released. A woman will test her urin in the morning. If the test is positive, she whould have the intrauterine insemination the next day.
Another method for timing an insemination is to artificially trigger ovulation. A medication called hCG can be injected by a woman when ultrasound determines that the egg or eggs developing in her ovaries are mature enough to be released. Ovulation will occur approximately 36 hours later. The hCG trigger injection is given in the evening and the IUI can be performed two morning later.