RobotStudio event

Re-setting the production hours since last service using the PCSDK

Hi 

Does any one know if it is possible to reset the production hours since last service? I would like to use the PCSDK to reset these hours instead of having to run the service routine to do this. I am able to read the hours by using:
 
myTimeSpan = controller.MotionSystem.ActiveMechanicalUnit.ServiceInfo.ElapsedProductionTimeSinceLastService

But I am unable to write to this. The reference docs state "public TimeSpan ElapsedCalenderTimeSinceLastService { get; set; }" so it states a set as well as get so I am guessing it is possible. But if I do this:

controller.MotionSystem.ActiveMechanicalUnit.ServiceInfo.ElapsedProductionTimeSinceLastService = myTimeSpan

At run time I get an exception. I am not sure what I am doing wrong.
Any help or guidance would be great.  

Cheers
Dave