noon

Specifies the exact time, 12:00 in the middle of the day.

Refers to the exact middle of the day, often with a literary or dramatic connotation.

all the time

Indicates the precise time of 12:00.

Indicates an approximate time near 12:00.

Indicates a deadline; at or before 12:00.

Indicates a duration of time continuing up to 12:00 (often considered slightly more formal than 'till').

Indicates a duration of time continuing up to 12:00.