You can do this easily with
Customisation > Custom Reports > New custom report
Dimension = Hour. This gives the desired result:
Note: this seems to be the hour-of-day in your timezone (Analytics account owner), and not the hours from the perspective of the different visitors around the world.
The latter is a different problem that I’m precisely searching a solution in Hour of day of a pageview/event/purchase, but in the visitor’s timezone?.