In Dark Souls 2, you can stand in Majula and look at clear skies to the horizon in all directions, including over Drangleic Castle. From there you can walk to the castle without loading screens and when you come out the mouth of a tunnel, it's night time over the castle in a thunderstorm. It's not like Bloodborne where a plot event changes the global time of day.
As for Firelink in DSIII, the ground around the fire itself with the rings in the ground look like Firelink from DS1. It's everything else that has been built up around it since then. I think at this point everything boils down to, reality in this universe is fragmented and shifting. Space distorts, things rise and fall, stretch and compress, dragging embedded sections of the environment with them.