Certainly sounds like Julian-day-hour-minute-second to me, just like all the timecode displays I've ever seen going back a good chunk of a century :-). I looked through the truetime schematics I have and none of yours match exactly so maybe some other brand. Some similar displays are sometimes used in video and movie editing and production (think those LED slates), although there the 3- or 4-digits would probably not be day, but some sort of sequence number, dunno for sure, I only briefly touched Hollywood :-) Tim.