grabbing mock time taken in Groovy scripts...?

I am a bit confused on how to get the time taken by the requests served by my mock, the one you can get here in the UI:
WebServiceMock/Message Log tab:
YYYY-MM-DD hh:mm:ss:ms:[operation] xxx ms

I am using context.getMockResponse().getMockResult().getTimeTaken(); in my Groovy script,
but it actually never works (I have runtime errors, I guess due to the fact I do not know where to correctly plug my Groovy script in order the method to be filled with some content, although I tried the event tab of the Project view and the script areas almost everywhere...).

any ideas would be very appreciated