interpretation of getCmTimeStamp

Does anyone know how to interpret the value returned by getCmTimeStamp?
It is in the tserver call monitoring events. It returns a Long value so I had assumed it
was some time in milliseconds/microseconds/nanoseconds but that does not appear to be the case.
There must be some format required to interpret the value.

I tried calling getTime for these events but it returns null.

Thanks for any ideas.
Andrew