Is it considered extremism to greet with the Islamic greeting upon waking or going to sleep, and must one obey one's mother in replacing it with other greetings such as "Good morning" and "Good night"?

Uttering the greeting of peace (Salam) is the best way for a Muslim to initiate interaction with his brother upon meeting him. The phrases "Good night" or "Good morning" do not substitute for the Salam, and one should not begin with them, as stated in the Hadith: "Whoever begins with words before the Salam, do not answer him." The preferable approach is to combine the Salam with these phrases. A Muslim can say the Salam silently and utter "Good morning" aloud if his mother does not understand the virtue of the Salam. Initiating with the Salam is a Sunnah (recommended practice), not an obligation. It is advised to appease your mother, be gentle with her, and choose words that please her, as long as they do not involve sin.