Would Jumu'ah prayer be invalidated if the Imam started his sermon one minute before the time due? And is one sinful if he says to himself, "Enough of this braying," in objection to the Imam raising his voice during the sermon?

First, scholars differed regarding the time for the beginning of the Friday prayer. The Hanbalis held that its time is the time for the Eid prayer, or the sixth hour of the day, while the majority held that its time is the time for Dhuhr prayer. The view of the majority is more cautious, but the opinion of the Hanbalis is strong. Therefore, praying behind an Imam who begins the sermon before the Dhuhr adhan is valid, even though it is more cautious to delay the sermon until the time for Dhuhr has definitely begun.

Second, raising the voice during the sermon is a Sunnah from the Prophet, peace and blessings be upon him, and one should not pay attention to whispers (waswas) concerning this matter.