I would like to know how to interpret the time_total_running property? This info is available in histogram.properties of the robot. Example of data : 188113353000.
You can open the log_history.txt in the software UR Log Viewer instead. Here you will be able to see the total time running correctly interpreted. 
This time is the time that the controller is ON. It does not mean that it was running a program necessarily so don’t use it to judge the life of the robot or anything related to that.
thanks Brentbarson. Is there another register that gives the operation time of the robot?
No, that’s sadly the only information we get from the UR controller. 
Thanks.
Feedback: This information was available previously (I believe it was with polyscope 3). Such info should be available: this is basic stuff.
I believe it was the same with CB3s. It just displayed the value on the Run tab.
But I agree. I have been missing this value before.