req42 is a framework for agile requirements engineering. Therefore, you can embed it in any agile process, like Scrum or Kanban or Lean Development. Or use it in conjuction with SAFe or LeSS or other scaling frameworks. It mainly ensures that good requirements engineering is much more than just creating and maintaining your product backlog.
Since req42 is mainly repository based - caring about the outcome, not the process - it does not prescribe when to work on which section. We claim that “req42 is process agnostic and tool agnostic”.