Outlook doesn't include a built-in method of creating an activity report, such as to show how many hours you worked on items marked with CategoryA and how much time was spent on CategoryB.
You can use a list view, copy and paste into Excel to do the calculations or use a third party reporting tool.
For tools to create reporting on Exchange server, see Exchange Server Usage, Reporting, and Analysis Tools.
The tools list on this page are used to create productivity reports.
Thank you for this.