The under-appreciated position of R. Avraham Gombiner on calculating the hours of the day
Rav Schechter reports that the Rav ztl, who followed Rabbeinu Tam with modern depression angle based humrot, was not concerned about any stringency that counting the hour of the day from alot ha-shahar would imply.
What is now abundantly apparent that this approach was the position of Ramban and the hakhemai sforad who followed.
Beyond the inability to apply the position of Magen Avraham in the afternoon to plag ha-minha for example at locations moderately far from the equator, we show that even in Jerusalem the approach encounters slight problems.
All of this is buttressed by an analysis of both R. Israel Isserlein, the Trumat Ha-Deshen, R. Avraham Pimential, author of Minhat Kohen and recognized by R. Gombiner, a contemporary, as an expert, and later authorities.
The approach suggested appears as well in the article on lighting candles in Jerusalem 40 minutes before sunset.
The manuscript’s first part is largely a tutorial introduction to this area of zemanim.
Critical to the above document is the following excel spreadsheet