Rav Aharon proves in his tshuvos [משנת רבי אהרן סי' ב] that the machlokes Gra [the Rabbi not the shul] - Magen Avraham [the Rabbi not the camp] whether שעות זמניות are calculated from נץ to שקיעה [Gra] or from עלות to צאת [Mg"a] depends on their other machlokes whether צאת is about 13.5 minutes after שקיעה [Gra] or 72 minutes [Mg"a and Rabbeinu Tam]. עיי"ש.
So he thought it was weird that in EY they are מיקל to do melacha on מוצ"ש like the Gra but are makpid on zman krias shma like the Mg"a.
What do you say??
