פירוש על ברכות 53:10

A distinction is drawn between tbe phrases "heat of the day" and "heat of the sun." The latter means the places in the sun are hot but those shaded cool; whereas "heat of the day" means that the heat is general, as at noon. "Heat of the sun" refers to the fourth hour, because before 10 a.m. even the sunny places are not excessively hot.

But although tbe Israelites were commanded to gather the manna "morning by morning," which according to R. Judah means up to 10 a.m., by that time it had already melted. The gathering had therefore to be done in the third hour.