I have a Eurail Select Pass. I know if you have a overnight flight (without connections or layovers) that departs after 7pm and arrives after 4am you can count it as one day, but if the connection is after 4am does it still count as one day or do you have to count it as two?
Using those rules you put the second day on the pass. Because the second day is already on the pass, any connections you make onto covered trains that day are covered. Example: Paris - Munich (don't know reality - haven't looked it up, its an example). Board in Paris at say 2300 on Tuesday, arrive Munich at say 0700 on Wednesday. Put Wednesday's date on the pass before you board the train. Sleep fitfully overnight. When you arrive in Munich your pass is all ready to go. Drag yourself over to the train to Nuremberg and your pass covers it. When you return after dinner to Munich its still good. Happy rails!!!