If periods are irregular, then begin calcium / magnesium at 14 days after the beginning of your last menstrual cycle, or simply take the supplement every day. (kellymom.com)
You may also find that your cycles are irregular at first. (babycenter.com)
If you have a small roof, or a roof that is irregular in shape or partially shaded by trees or other buildings, you might want to consider smaller, more efficient panels. (solar-estimate.org)