a.) Simple day/night switch. Click a button and/or take 2 short rests and everything everywhere transitions to night. LR'ing then transitions it to the next morning.
Seems you didnt read that post to the end (excluding spoiler) ... did you?
I described there exactly the same as one of possibilities for D/N system.
That's true, my bad. I saw the spoiler didn't read anything below it. My bad!
I asked if you can imagine time flow that would "support that map design" ... this time flow would completely ignore map design. :-/
I disagree with the premise that location-dependent time flow is necessary to support map design.
Are you really claiming that so many players will be outraged enough to ruin their game experience AND negatively impact Larian's final sales if, e.g., time doesn't pass at 10 seconds per second in the Grove and 20 seconds per second while traveling between regions?
Depends ... [...]
Problem with this is not "in the Grove" and "outside the Grove" ...
I was also talking about this abowe ... it would be more like 1s=10s in Grove ... 1s=1000s outside the Grove somewhere ... 1s=100s outside the Grove somewhere else ... etc. > that is the problem, inconsistency.
Also, it all goes only as deep as you let it ...
Sure, nobody would notice that 6 hours passed ingame while you were exploring the Grove ...
But dont you think some eyebrows would be raised if you would enter Windmill basement at 12PM and get out at 6AM?

Or the same during exploring Blacksmith basement? (Without spider caves.) Or that going through Zevlor's Cave, or talking to Kagha and Nettie would take you 4h of ingame time?

First of all, I don't think that such time scales need to be so highly different. IF the time scales do *need* to be different, then a factor of 2 or 3 is perfectly fine. Everything does not need to be modeled
exactly perfectly; don't let the perfect be the enemy of the good.
Second, I don't think times scales need to be different at all. It's not needed. Use a simpler system that is mostly immersive, rather than an incredibly complex system that might be more immersive on its own, but not necessarily when taken into account map size.
Third, why would the game work such that spending like 5 minutes in the Windmill lead to 6 hours??? You'd be inside a building - a dedicated area with no access to the outside roads - so clearly the game time should be passing much more slowly. 5 minutes in the Windmill should be like 30 minutes in-game, max. Similarly, the Blacksmith's basement, Zevlor's Cave, and talking to Nettie and Kagha are all self-contained zones and shouldn't have significantly sped-up time progression. Game time could even stop during dialogue for further time consistency.
tl;dr: I think you're vastly overcomplicating a proposed time progression system, in such a way that would generate lots of unnecessary problems. Also, you're exaggerating those problems to make them seem worse than they are.