Hi @EdP
Thanks for posting your question!
I suggest considering using the Issue Cycles for your use case. Here is a documentation page that will guide you how to import the issue cycles - Issue cycles. You should simply add the status you want to group together and once you import the Issue Cycle, eazyBI will import several measures and properties that you can use in your report, including the average time the tickets spent on those statuses. You can also check out this community post - Count issues that passed by certain status and not closed - #2 by QiZhang that has some screenshots as well.
Best wishes,
Elita from support@eazybi.com