毎朝 and 毎晩: repeated mornings and nights
Separate when an action repeats from how long each occurrence lasts.
Every morning
毎朝 (まいあさ) means every morning. 「毎朝、新聞を読みます」 describes the habit of reading the newspaper each morning.
「毎朝六時に起きます」 additionally gives six as the waking time. 毎朝 alone does not specify an exact hour.
Every night
毎晩 (まいばん) means every night. 「毎晩、日記を書きます」 says the speaker writes a diary each night.
「子供のころ、毎晩本を読みました」 describes reading every night in childhood. 毎晩 does not necessarily mark a current habit.
Frequency and duration
「毎朝三十分歩きます」 means walking for thirty minutes every morning. 毎朝 gives frequency, while 三十分 gives the duration of each walk.
「毎晩ではありませんが、よく電話します」 says calls are frequent but not made every night. Do not expand the partial negation into never calling.
Does 「毎朝三十分歩きます」 mean walking all morning?
Show the answer and why
No. The walk repeats each morning, but its stated duration is thirty minutes.