Late hefsek on Thursday

I did a Hefsek Tahara after sunset, but before Tzait Hakochavim. I did the Hefsek at 8:25. Sunset was at 7:50, Tzait was at 8:32. Can I use this Hefsek? I am trying to become pregnant, and not using this Hefsek will mean I would have to go to the mikvah on Friday night. Since I will not be able to do that, my immersion will be postponed 2 days, until Sat. night, and I am concerned that I may miss my ovulation date.
Thank you in advance for your help:

Dear questioner,

Thank you for your question.

Unfortunately, a hefsek taharah performed 35 minutes after sunset is too late and you may not begin counting the seven clean days the following day. 

If you performed a thorough bedikah at any point earlier in the day (before sunset) or even the day before, you may count that bedikah as the hefsek taharah and begin counting the clean days on Friday if the bedikah was acceptable.

We recommend that you make a practice of performing an additional hefsek taharah in the morning. If you forget to perform one before sunset, you may generally rely on the hefsek performed earlier that day.

We hope you can make extra efforts to arrange a Friday night immersion. Even if the mikvah is not open on leil Shabbat, you can check if they will make special arrangements to open the mikvah for you. If the mikvah is far from your home but still within walking distance, you can drive there before Shabbat and walk home after your immersion. If you are unable to arrange a Friday night immersion, then unfortunately, you have to delay your immersion until Motzai Shabbat.

Please feel free to get back to us with any further questions.

This internet service does not preclude, override or replace the psak of any rabbinical authority. It is the responsibility of the questioner to inform us of any previous consultation or ruling. As even slight variation in circumstances may have Halachic consequences, views expressed concerning one case may not be applied to other, seemingly similar cases.

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