how do I make a report showing the length of time between task completion

Hello,

Are you looking for the duration of the task? That is automatically captured in the "Actual Duration" field in the overview section. 

when you ask "how long" does it take for one task to be checked off -- I think what I would like to get clear about is when you would want to "start the clock".

While Workfront does provide a number of ways to calculate the task's age, it's fair to say that this often relies on assigned users to indicate when the clock has started. If you're trying to say that your users are a bit lax in that department (don't track time, don't click "work on it/done", don't update dates), I would probably suggest the following link.

https://experienceleague.adobe.com/en/docs/workfront/using/manage-work/tasks/task-information/handoff-task-date

If you're able to make handoff date work for you, then you can look into calculations like the one shown in this previous post:

https://experienceleaguecommunities.adobe.com/t5/workfront-questions/is-there-text-mode-to-get-the-sum-of-a-calculated-date/m-p/475938#M8767

@janellecurry Just checking in — were you able to resolve your issue? We’d love to hear how things worked out. If the suggestions above helped, marking a response as correct can guide others with similar questions. And if you found another solution, feel free to share it — your insights could really benefit the community. Thanks again for being part of the conversation!

I understand what the other posters said, but I think my issue is that I want to do a report looking back over the last year. We're leaving Workfront in October and I won't be making new updates to calculated fields. 

My issue is that we need to show how long the program review task in projects lasts so we can have leadership crack down on review turnaround time. 

Is there a way to do this for projects from the last year? I'd like to see program review task duration, portfolio, program, and category name.