Hello,

Well the easiest answer would be to compare pxCreateDateTime with the resolution date time but this will not be sufficient for you I guess.

The next approach might be to work on implementing a sort of timer on each task but I don't think we have that Out-Of-The-Box

You can have a custom property defined on those tasks you wish to know the time duration. Lets say Task A is there. As soon as the flow starts for your task A, have a property TaskA_StartTime=Current time stamp. Similarly, you can have TaskA_EndTime=Current timestamp. Do a property set at your appropriate place. Now, you can use the time difference.

This can be set as your work status changes. You can further tweak to get the requirement done.

OOTB i am not aware of any such thing available. 

Instead of creating these properties, you can get the value from the history table. In history or audit you can have specific msg and then you can query on that msg and the timestamp. 

Hope this helps.