If you are Sefardi, you may rely on the ruling of the Shulchan Aruch which permits a
four day minimum before counting the
seven clean days.
If you are Ashkenazi, the five day minimum may not be reduced to four days except under extenuating circumstances. For example, if you consistently
ovulate on day 11 (as confirmed by ovulation kits, etc.) and you are trying to conceive, there is room to permit reducing the five day minimum to four days. If the only concern is that it is challenging to immerse on Friday night, unfortunately that is not sufficient cause to permit reducing the minimum days.
We may have useful tips or advice to help make a
Friday night immersion easier, so feel free to get back to us with more details.
B'Hatzlacha!