Date last modified

I don't know if this is possible, but I have to ask.

I'm building a Storyline 360 course that will have to be periodically revised and timestamped with the revised date. The "Revised by" date will display on its own slide in my course. Is there any script, or trigger, or anything I can do to display that date and have it only change whenever the course is republished, or do I just manually enter the revised date whenever I republish? ...I know, looking for magic here ;) 

Thanks for every response,
JB