2 weeks before next. Assuming you have regular, predictable cycles, ovulation occurs around 14 days before your next scheduled menses. Example, if your cycle length (day 1 to day 1) is 28 days, then ovulation is most likely day 14. Sex days 12-15 are best for conception. If cycle is every 30 days, then ovulation likely around day 15/16. Also, consider the use of home ovulation tests to guide you.
Depends. Pregnancy has been documented from exposure on any day of a woman's cycle including during menses. For most with regular cycles it would be mid cycle. Those with irregular cycles/ovulation are more likely to have unpredictable conception dates. Whether there is time or a site for the conception to attach & thrive is unpredictable. Some cite that as many as 1/3 are shed before pregnancy is evident.