I’m not sure exactly what you are trying to do, but if I understand correctly, you want two timestamps? One in the beginning of a process and one at the end.
At the beginning of the pipeline, create a map object, and add a transformer (pub.date:currentDate) to obtain the date/timestamp value. Map it to the variable StartTime
At the end of the pipeline (or where relevant), insert another map (or cut and paste) and map the timestamp value to a new variable called EndTime.
Now, if you want to obtain the elapsed time, then you will probably need to build a java service, input the two values and use the java utility to determine elapsed time. I am not a java guru, but I know this is possible, and even I could build it, so I do not think you will have a problem.
Hope this helps.