Today and Twenty-four hours

Today noun - The day that includes the present moment (as opposed to yesterday or tomorrow).

Twenty-four hours and today are semantically related. In some cases you can use "Twenty-four hours" instead a noun "Today".

Twenty-four hours noun - Time for Earth to make a complete rotation on its axis.

Today and twenty-four hours are semantically related. Sometimes you can replace term "Today" with "Twenty-four hours", this terms are similar.