Hmmm. I do not have what is here so I looked at what TNT has, 73 minutes 23.976 fps. That is definitely a big difference, and NOT due to a framerate speed-up. However, I also know that pictures at IMDB include studio promotional pictures that are not necessarily taken from film scenes. If that whole scene is missing, that is a real problem. But it may just be a staged shot, or an alternate take. Deadman discussed that sort of thing in another recent thread.
Unless there is video evidence of an actual longer version, I suspect the supposed 78 minute runtime is a much-repeated error. There are other sites that list different times. (Which can also be wrong.)
80 min:
https://www.rottentomatoes.com/m/hand_in_hand
73 min:
https://letterboxd.com/film/hand-in-hand-1961/
73 min:
https://www.themoviedb.org/movie/266108-hand-in-hand