what about like "Piano Stories" then?
See it depends on whether there's a connection between the 'movements'. In the case of a sonata usually things are pretty clear, and the movements ARE connected. In the case of suites, usually there is a theoretical and philosophical idea behind the suite, or perhaps a single idea of 'dance', but that isn't really all that strong, for me, to call it a single work.
For another example, what about variations? Rwezksi's "People united will never be defeatd" is some 40 minutes long variations (LOTS of them) but it certainly is a single work. Same goes for a movement of Brahms symphony (4th I think, but can't be sure)...
In other words it's difficult to tell and even more difficult to judge.
But due to be recent experience with "Piano Stories" I do think that this IS a single work and people tend to take it as such. There's no valid reason to take up the whole work, and not single 'movements', but for me it would feel incomplete. Perhaps I'm too attached to this and rather preoccupied, but none the less it seems that each movement requires the next to carry on successfully.