To avoid worrying about such questions, just look at the result after the game: after "congratulations, victory!", a table appears with your result, which includes the number of days it took to complete the map.
Because what Kyle is talking about is just a specific case. If you were playing as red on this map, the victory would be dated on day Z, not Z+1...
P.S.: Another technical point. How do you fire a hero who is in a castle if he entered it on the last turn? Should I just leave him there?