In my experience, a leisurely playthrough of Ori and the Will of the Wisps takes around ten hours. But it's possible to finish it in an hour, as speedrunner Isaia has proven above.
The game only released last week, so there's plenty of room for improvement with this any% run. For reference: the world record for predecessor Ori and the Blind Forest is just over ten minutes, and while Will of the Wisps is a longer game, I'm predicting the record will improve dramatically.
The run implements a "sword leap glitch", which permits jumps that would otherwise be impossible. Isaia explains on reddit that you need the sentry and sword equipped. Once equipped, you need to "press sentry then sword quickly. The shorter the gap the more height you get."
In his Ori and the Will of the Wisps review, Tyler wrote that it's "inconsistent and sometimes annoying, but ultimately a charming, challenging, heart-string-pulling fable."