Actually the best day to conceive would be 2 days before ovulation, because most of the swimmers that made it to the tubes are still alive, waiting for the egg to be released. The day before is also a very good day; basically you want to give yourself at least 12 hours between intercourse and ovulation, so the swimmers are in position and had time to do their capacitation. DD was conceived 3 days before O, and with this one we DTD 2 days before and the day before.