朝 and 昼: morning and daytime
Distinguish time-of-day ranges from the midday meaning supplied by context.
Morning activities
朝 (あさ) means morning. 「朝、窓を開けます」 describes opening the window in the morning.
「朝から雨が降っています」 says it has been raining since morning. から marks the starting point.
Daytime and midday
昼 (ひる) can mean daytime as opposed to night, or the period around noon. 「昼は暖かいです」 says it is warm during the day.
「今日の昼に会いましょう」 can suggest meeting around lunchtime today. Setting an exact time separately makes the arrangement clearer.
Starting points and endpoints
「朝から昼まで働きました」 means working from morning until midday. These broad time expressions alone do not give an exact number of hours.
「昼までに戻ります」 promises to return by the agreed midday point. Distinguish a duration ending with まで from a completion deadline with までに.
Does 「朝から昼まで」 establish exactly four hours?
Show the answer and why
No. Without exact start and end times, the duration is not fixed.