The duration between when a pull request is opened and when it is merged.
Why it matters: Time to Merge is an indicator of how much inventory your team is managing at any given point in time. High inventory requires additional overhead to manage and increases context switching across the engineering team. Low Time to Merge is usually correlated with a higher Pull Request Success Rate and lower Cycle Time.
How to use it: When this metric is high, it’s usually a good time to re-evaluate collaborative processes. It may be that the latter end of the software delivery process has too many bottlenecks. To diagnose where work typically gets stuck, look at the component parts of Time to Merge, such as Push Volume (before the code review process), Review Cycles and Review Influence (code review process), and Pull Request Success Rate (after the code review process).
Note that while it may be tempting for your team to increase the Time to Open to decrease the Time to Merge, this actually has the inverse effect. Pull Requests that have a lower Time to Open get through the Review Process faster and are merged sooner.