Do you two actually love each other, deep down? o_o
Focus on the topic please, not the people.
That's my main... I can't think of the proper descriptive word for it. Not concern, but like... Reservation towards optimism of seeing Day/Night related systems? Assuming that atmospheres and how lighting is handled in BG3 is similar to Original Sin 2, then the way you'd even begin to making day/night features is strictly stuck to that. Though implementing Raytracing (Specifically global illumination, or RTGI for short) would need to at the very least rework that, which inevitably would break the design in how you'd make weather-based interactions as it is right now.
The coordination and code for that is a significant tongue-twister too, to keep things in order. The way it works is that you have "atmosphere triggers" which is an invisible box you assign to a specific area. Each area has its own light probe that maps out the lighting in that specific area. This area can have multiple atmospheres (think different weathers and lighting configurations eg. daylight or night) with one active at a time. You can swap between these through scripting, with a set transition timer between the atmospheres. You could set this transition to any length, but it's pretty performance intensive if you make it really long. So to make a day/night system for that game specifically, you'd need to add these atmospheres for each area individually, and write scripts that change all of these individual areas' assigned atmospheres. A time tracking solution would need to be made too, potentially with some modularity (as Tuco mentioned somewhere earlier, what about turn based events or if only a part of the party is in turnbased?). You could use really long timers, but that comes at a cost of performance too.
Point being, there's a lot of variables to keep in mind even at a glance, and all of would possibly need to be binned or heavily reiterated at the trade for RTGI. Though the other way around, redesigning the atmosphere/light probe systems could make it a slightly less daunting task, but if that's one of the last things to be done, then you might wonder what worth it would be if nothing else is made to recognize and make use of the day/night cycles. Again I want to stress, that's my thoughts based explicitly on comparing my experience with Original Sin 2, where I've been making a weather system for narrative reasons of my own, and it assumes that it's similar in BG3, which may or may not be the case.
I have a huge soft-spot for lived in and breathing worlds though, Zelda: Majora's Mask still remains a personal favorite just for the different activities and schedules the citizens were on, which was complimented very well by the game's time loop feature. So I'd be really excited to see some day/night passage of time too. But I can see many reasons why the idea could ultimately be decided against too.
