First, be specific.
Figure out exactly what information is needed and exactly how accurate is needs to be including units. Understand when the log will be recorded and/ore reset. You only have 1k in a ML1000, so you can only do so much. It's easy to record things like:
Total Time Running (XIC RUNNING_BIT RTO RUN_TIME)
Total Time Stopped (XIO RUNNING_BIT RTO STOP_TIME)
Number of times started (XIC RUNNING_BIT CTU START_COUNT)
Number of times stopped. (XIO RUNNING_BIT CTU STOP_COUNT)
From those few values, you can calculate average time running and average time stopped, and do quite a bit of analysis.
If you need to log the individual occurrences with a timestamp, the ML1000 is going to limit you with it's 1k user ram. If you absolutely must log to this level of detail, you're better off buying a datalogger, or a Panelview or other operator interface with that capability.