Ovulation is the time of egg release. This occurs at one moment in time and signs occur for several days. An outward sign is the production of more mucous than usual. The rhythm method of consciously not conceiving would take signs of ovulation as days not to have intercourse.
Different women ovulate at different times in their cycle.
If one wants to rely on the cervical changes, a good book to read is A New View of a Woman's Body . It describes changes in the cervix and what exactly to look for in different women. Although one can just start looking inside and see the changes for oneself. Remember that every woman is unique in how her body works. Do not rely on other people's information to notice the changes in your own body, because these changes are not only physical.