A team asks how much time to allocate to Product Backlog refinement and when it should be scheduled. What does the framework say?

• ARefinement is a Scrum event with a timebox of four hours per month.
• BRefinement is an ongoing activity rather than an event. Scrum prescribes no timebox and no schedule, and the Scrum Team decides how and when it happens.
• CRefinement must take place immediately before Sprint Planning.
• DRefinement is the Product Owner's individual responsibility and does not involve the Developers.