If your period started on Motzei Shabbat, the fifth day is Thursday and that is the day you should perform your hefsek taharah (if the bleeding has stopped by then). You would then be scheduled for a Thursday night tevilah.

Unfortunately, even given your travel schedule, you may not perform your hefsek on Wednesday and begin your seven clean days on Thursday. Depending on when your flight is on Thursday night , you may be able to immerse before going to the airport as nightfall is rather early at this time of year. There is even room to permit immersion after sunset on Thursday instead of waiting until nightfall. You should call your mikvah in advance to make arrangements with the mikvah attendant.

If you are unable to immerse Thursday night due to your flight, unfortunately you will have to delay immersion until Friday night.

If there are extenuating circumstances that would make this delay especially challenging for you, please get back to us with more details.

B’hatzlacha!