How long does it take for yaz (drospirenone and ethinyl estradiol) to become effect(without condoms&prevent preg)? if i take the pill (for the first time) on the first day of the period

Some thoughts...: If the Yaz (drospirenone and ethinyl estradiol) is not fully effective that first pack of pills (or maybe the first 2 packs), then a woman might ovulate. If she ovulates, then she is fertile around ovulation, which is about days 11-16 for a very regular 28-day cycle. But, she is not fertile (due to her period, not due to starting yaz (drospirenone and ethinyl estradiol)) when she is having her regular period of 5 days or so, when she first starts her first pack of yaz (drospirenone and ethinyl estradiol).