I have created a Workbook where the users can enter the tasks to be performed.

I want to add a function that calculates the time elapsed and i have the following requirements:
1. When the cell value under "Status column" changes from "Open" to "WIP", the timer should start.
2. When the cell value changes from "WIP" to "Pause", the timer should stop.
3. When the same cell value returns to the value "WIP", the timer should resume from where it had paused.
4. When the cell value changes to "Closed", the timer should finally stop and tell the total time elapsed on the task.
5. The timer should keep running even if the excel file is closed (Because i am not able to give access to multiple users on the same file).

Can anyone help me please?