You can modify the response level to have more than just one 'clock'. For example you could have one that measures from open to resolved and another from open to inprogress or indded from inprogress to resolved.
If the origonal response level is changed during the process, then these clocks will be recalculated for you.
But how do I define two clocks.
Do you have access to the LDSD documentation CD? The pdf called LDSDAdministrator? Without that you are going to be working very hard! The section in there called Response Levels talks about creating Escalations and that is what you will probably need. Another Escalation for those for each 'clock' you want to measure in a process. If anyone in your ccompany has been on the core administration course, I'd see if they still have the notes as there are plenty of examples of this in there.