In this shiur as well as others in the past, I note that Rebbe doesn't address the following: Chatzot Hayom should be 1/2 of the day, whether it's netz-shkia or alot-tzet, the same astronomical phenomenon, the middle of the east-west bow. If the day is alot-tzet, then the only way this would happen is if the morning and evening ben-hashmashot are the same length. Since alot-netz is for sure 4 mil, then this requires saying ben hashmashot (eve) is also 4 mil. Meaning, if you pasken M.A. on figuring shaot zmaniot, you must pasken R.T. and Rishonim for tzet. And vice-vera: anybody not doing 4 mil tzet is doing an inconsistent chumra yeteira being machmir M.A. zman kriat shma, etc. I first saw this pointed out by Harav Min Hahar (late rav of Bayit Vegan). Rav Moshe has an answer to this by redefining chatzot but I don't understand it nor how it fits what Rebbe quotes as Rav Moshe's fixed equinox chatzot. Respectfully, Steve Weisberg