Kingdom Come: Deliverance has some problems, but its quaint countryside certainly isn't one of them. In fact the map is maybe the nicest thing about the entire game, so let's all see how long it takes to walk across it, taking in the sights and trying not to fall off a rock and break a leg.
This video, by How Big is the Map?, shows us... how big the map really is, by starting in one corner and walking all the way to the opposite side. It's mostly in a straight line, but given the fact a fall will break bones and slow you down, and that combat with an NPC could end your entire day real quick, there are some quick detours for the sake of self-preservation.
For those just after a number, it took 1:10:27 at walking pace to cross the whole map.