Although it is true that refinement should not take more than 10% capacity of the Development Team,
this question was not specific about the Development Team but the activity of Product Backlog
refinement in general. The Product Owner is responsible for maximizing the value of work that the
Development Team does, thus he needs to spend as much time necessary keeping the Product Backlog
healthy. This may require feedback from the team. A bit of a tricky question. :)