Project Status Timers

I would like to calculate how long a particular project has been in a certain status. Example: Status -> Draft, In Review, etc.

I created a new module named Project Status Times. I was able to create a Workflow that would create records in Project Status Times every time the status of a project changed.

Project Status Change -> Creates -> Project Status Time Record -> Project # - In Review - 7/30(Date) - End Date???

I am unable to find a way to enter an end time. I can only create Start times for when Project status changes.

Any ideas?