In OSA, any practice that aligns with the Agile Manifesto is a candidate practice to experiment with.
The Manifesto says to “deliver working software frequently” and also “at regular intervals, the team reflects and tunes and adjusts its behavior accordingly”.
In light of the foregoing, during an OSA implementation, we can reasonably expect teams to engage in iterative and incremental development of software. For most organizations, this strongly implies the use of time-boxed iterations.
This is not to say that Scrum must be used, or even that iterations are required. The numbers 1 through 8 in the OSA diagram are suggestive of iterations, even though the method does not strictly require that any team must use them.