I think the point is, though, that as long as they are all unsigned longs, if millis() were to rollover. Then when you subtract timeEarlier from timeNow, it will rollover backwards and still give you the difference. The only thing that would mess this up is if you tried to subtract more than 49 days, then your actual calculation would "rollover". But like I said, I'm not worried about that. I'm only worried about millis() rolling over.