* The Sprint Planning is an event that occurs at the beginning of each Sprint, where the Scrum Team plans how to deliver a valuable product Increment. The Sprint Planning consists of two topics: What can be done this Sprint? and How will the chosen work get done? The outcome of the Sprint Planning is an agreed-upon Sprint Goal, a Sprint Backlog, and a plan for delivering the Increment.
* The timebox for the Sprint Planning event is proportional to the length of the Sprint. For a one-month Sprint, the timebox is 8 hours. For shorter Sprints, the timebox is usually shorter. The Scrum Team may decide how much time to spend on each topic within the timebox, depending on their needs and preferences.
* The timebox for the Sprint Planning event ensures that the Scrum Team does not spend too much or too
* little time on planning their work for the Sprint. The timebox also ensures that the Scrum Team has enough clarity and alignment on what and how they want to achieve during the Sprint.
References:
* Scrum Guide: https://www.scrumguides.org/scrum-guide.html
* Sprint Planning: https://www.scrum.org/resources/what-is-sprint-planning

A Product Owner should not measure product value by the increase in the team's velocity. This is because:
Velocity is a measure of how much work a Scrum Team can deliver in a Sprint. It is based on the estimation of Product Backlog items that are selected for a Sprint and completed according to the Definition of Done.
Velocity is not a measure of product value. It does not reflect how well the product meets the needs and expectations of the customers, users, and stakeholders. It does not reflect how much value or impact the product creates in terms of revenue, satisfaction, or social good.
Velocity is not a goal or a target for a Scrum Team. It is a planning tool that helps them forecast their future work based on their past performance. It is not a metric that should be used to compare or judge teams or individuals.
A Product Owner should measure product value by using indicators that are relevant, meaningful, and actionable for their product context. These may include metrics such as customer feedback, usage data, market share, return on investment, or social impact.
Reference:
[Scrum Guide], page 7, section "Developers"
[Scrum Guide], page 10, section "Definition of Done"
[Scrum Guide], page 15, section "Sprint Backlog"
[Professional Scrum Product Owner Training], page 5, section "Product Value"
[Professional Scrum Product Owner Training], page 9, section "Business Strategy"