According to Rebbi Akiva, five complete onas are required, to be completed with the sixth when missing part of the fifth. In this case, the sixth will inevitably be of a different nature than the fifth (one day the other night) with a different length. How can one compensate for the other?
Meraimar responded that there was actually no Tvul Yom present at receiving the Torah. Can this be proven from a source, or was it known from tradition?
1) Rebbe Akiva counts Onos, not days/nights. If Tuesday can compensate for Shabbos, day can make up for night — unless I am missing something in the question.
2) It can be taken the other way around. First Abaye Bar Ravin and Rav Chanina Bar Avin said that the Torah was given to Tevulei Yom. Ravina wanted to know if that was a fact or a possibility. Mereimar answered that it is a possibility. However, Rashi does say it as a fact, that nobody had to Tovel on Shabbos. Perhaps we can derive this from Moshe Rabbeinu’s calculation when he broke the Luchos.
Rashi says here that the reason the Torah did not care about Tevulei Yom is because that is only about Kadshim. The Gemara later says that Moshe broke the Luchos because he associated getting the Torah with eating the Pesach. So, although AL Pi Din the Torah could have been given to Tevulei Yom, obviously that is not optimal.
Also, it is a Sevara, that once the Torah was Makpid on this particular Tuma, it was worked out to be optimal. That is what prompted the question in the first place.