I think I knew it at one point but had forgotten ~
"Scenes from the film that were set in 1912 ran two hours and 40 minutes - the exact time it took the real RMS 'Titanic' to sink."
~ page four of "Titanic:The Tragedy That Shook the World /Plus: The Movie Remembered"
(even though there are way more Titanic movies than one movie to be remembered; and they are mentioned in the publication, too)
I think it's fascinating about the two-hours-and-forty-minutes running time of the 1912 scenes. And I forgot that movie itself is three hours and fifteen minutes.