How to save clock based on each Assignee change individually


I am using HP SM 9.41 codeless. I want to set the clock for each individual assignee change, so that I can track how many minutes each of them have spent to resolve the particular call. I have seen that there is a clock file in the db. But i could not use it properly. 

It will be much helpful, if somebody helps me out of this.


Thanks in advance,