Customer Discovery+Validation combined with Scrum, how?

When you have a startup that essentially does a Web App, there is a set of methods that everybody seems to agree on: Customer Development and Agile Development.

Agile Development is really clear, many people have written thousands of blog articles and books about how long iterations should be, how to process feedback (User Stories, Tickets) and rules throughout the iterations. E.g. not to change the plan during a sprint.

But what about Customer Development? Essentially I could only find very high level descriptions, even after hours of googling:

1. Customer Discovery (test hypotheses, continuous discovery)
2. Customer Validation (make customer validate the solution); go back to 1. with a new Pivot in case we are not enough satisfied
3. Customer Creation
4. Customer Building (mission complete)

This all makes a lot of sense, at least on a high level. But in reality:

• How big should the Pivots be? Work for one week? One month? Possibly throw away everything?
• How much can or even should the Pivots be synchronized with the Scrum process?
• How do you tell when a Pivot succeeded? 100% retention? When does a Pivot fail? 0% retention?
• How much should or may Pivots replace existing parts?
• For Customer Discovery, would it be enough to write user stories and break them down to tickets?
• For Customer Validation, would it be enough to look at hard metrics, i.e. conversion and retention?