By the time you see a thermal shift on your chart, it is usually too late to conceive that cycle. Ovulation occurs on the day before your temperature rises. The best times to have intercourse are the few days before you see a thermal shift on your chart. A single rise, however, does not always mean that you have ovulated. You need to see a clear and sustained rise to confirm ovulation, so do not stop having intercourse until you see several elevated temperatures and ovulation is confirmed.