Two numbers worth tracking
Hours to first review shows how long authors wait for someone to look at their change. Hours to merge shows the whole cycle, including rework. Track both per repository, because one slow repository hides behind a healthy organization average.
Use the median, not the mean
A few pull requests left open for weeks drag an average far from what a typical change experiences. The median hours to merge describes the usual case. Keep the long tail visible as a separate list of the slowest pull requests.
Get the timestamps out
The export gives you created and completed times, hours to first review and hours to merge for every pull request, and a Summary sheet with the median hours to merge for each repository. Add a pivot table in Excel if you want to split by author, month or target branch.
Read the result with care
Draft pull requests, abandoned pull requests and automated dependency bumps all distort the figures. Filter on status and author before you present a number to a team.
Get merge timing without writing a script
The Summary sheet reports median hours to merge per repository straight from the export.
See PR & Pipeline History Export for Azure DevOps