I will likely be able to go to the mikvah this Friday night. The nearest mikvah is a 45 minute walk from my home, and I have to bring a friend to be a shomeret. I am sephardic and my husband is ashkenaz. I believe that the allowable time for tevila is significantly earlier for sephardim than for ashkenazim. Would it be permissible for me to immerse at the earlier time this shabbat and in general? Thanks for your help.