How to calculate time spent on the record in a Salesforce case queue?

I have created three fields on case object: case1-datetime, case2-datetime, case3-datetime.

Whenever a case is created we need to calculate the time spent on the record (queue1) – it will store the value in case1 field.

Whenever I change the one queue to another queue, I need to calculate the time spent on that queue. Then again the second queue is assigned to the first queue. (it will store the value in case2 field).

Then the first queue is assigned to the third queue, then calculate the time spent on the third queue. Then calculate the overall time spent on the all the queues. (overall time spent is fill with case3 field)