"Ovulation predictor kit (LH kit)
The detection of the LH surge has become useful for people who want to know when ovulation occurs. LH can be detected by urinary ovulation predictor kits (OPK, also LH-kit) that are performed daily around the time ovulation may be expected. The conversion from a negative to a positive reading would suggest that ovulation is about to occur within 24-48 hours. Couples who plan to conceive would time intercourse accordingly.
As sperm can stay viable in the woman for several days, such tests are not recommended for contraceptive practices."
Hope this helps--- I always thought that from the surge (a positive test) that is when you are ovulating but in fact it is the Surge that causes the release of the egg- so has they say it is within 24-48 post surge that the egg is released.