Until What Time May One Eat Pas Shacharit?

Shalom u-vrachah,

One may eat pas shacharit until four seasonal hours (each seasonal hour is 53 minutes) from the time one rises. For a Torah scholar who is occupied with his learning, this is until six seasonal hours from the time one rises. This applies specifically when he has not tasted anything in the morning; however, if he has tasted something, he may eat pas shacharit even afterward.

Sources: See Shulchan Aruch, Orach Chaim (siman 157) and Mishnah Berurah there. However, the view of the Yaavetz in Mor U-Ketziah there is that the calculation should be made in equal hours and not seasonal hours. And in Sefer Shulchan HaTahor it is stated that the calculation should be made from dawn and in equal hours. The Kaf HaChaim (seif katan 2) brought in the name of the Mateh Yehudah that in all cases we calculate from dawn and according to seasonal hours.

With blessings,

Hillel Meirs