Moshe's added day of preparation - the primacy of Torah sheBa'al Peh

If, as the gemara suggests (Shabbos 87), the instruction of 'vkidashtem hayom u'machar' did not mean to start counting from the day Moshe heard the command, but meant to start counting from the day after (the extra day added m'da'ato), then why does the pasuk use the confusing term 'hayom' instead of making that explicit? And, as the Magen Avraham asks, why do we refer to 6 Sivan as 'zman mattan Toraseinu' when the Torah was not given until 7 Sivan because of this added day? The Sefas Emes answers b'derech derush that klapei shemaya the preparation for giving the Torah complete on 6 Sivan, but the actual giving was delayed because of Moshe's addition of a day. Since each year Yom Tov brings with it a renewal of spiritual energy of that original zman, we today experience and must prepare for that moment of readiness to give the Torah which occurred on 6 Sivan, and it is to us that the Torah addresses the instruction of 'hayom u'machar'. In a less mystical answer the Kli Chemdah*** in the introduction to his sefer writes that heeding Moshe's interpretation of torah sheba'al peh that 'hayom u'machar' meant 7 Sivan was itself a kabbalas haTorah on 6 Sivan. Accepting the authority of Chazal as interpreters of the Torah was the foundation upon which giving Torah sheb'ksav rested. He relates this idea to the debate between the Perushim and Tzedukim over when to begin the sefira count. Unlike the Tzedukim who counted sefira only from the day after Shabbos, the Perushim began counting from the day after Pesach davka so the count would finish the day before kabbalas haTorah to reinforce this idea of the primacy of torah sheba'al peh.

*** thank you Bill Selliger for this mareh makom
One side note: the Bais haLevi writes that had BN"Y not done cheit haeigel, there would only have been a torah sheb'ksav which included everything. Yet, here we see that even in preparation for mattan Torah, a 'ba'al peh' interpretation was required. Yesh l'yasheiv...