How is a clock, lighting and rain "a huge workload"? If Larian said this is "out of the question" then maybe WotC shouldn't have granted a licence. Half arsed homebrew DOS like BG3 isn't something I would have paid early access for, end of story. I said if before, everytime something is changed, not implemented, homebrewed or removed because Larian can't be arsed, a game based on the D&D lore and rules becomes....well not based on D&D. I understand devs have artistic licence and require some freedoms and I don't want a 1:1 creation of the 5e rules if it doesn't work. However if you don't even bother implementing the rules to begin with how can you argue against it?
If you can make it dark inside why not outside? Implement a moving light source from above over a finite period then.... make it go away, sounds pretty easy to me. I don't even care if everyone just does what they do during the day or sleep on a roll next to their position. This isn't a small feature you can dismiss out of hand especially if it affects so much of the race lore. You will never see Drow in daylight unless dragged kicking and screaming, ever. Nor will they attack a settlement outside the dead of night. Tadpoles are becoming more McGuffin cheese story telling by the day.
Making a McGuffin the apparent cause for all the deviation from D&D is cringey af. The tadpole makes you warp to camp at night and warp back in the morning, the tadpole makes Drow and vampires daytime creatures, the tadpole makes it daytime all the time, the tadpole makes lv 1-3 goblins opaf with 20-30hp, the tadpole makes a 6 inch step a 9th level class advantage, the tadpole gives mages backstab advantages, the tadpole gives piles of specialist ammo and bombs to mundane garbage one hit mobs, the tadpole makes a DOS clone and calls it BG......so on and so forth.
I understand there is a need to please console players and speed runners. They want DOS3, pretty sure you can fudge a few numbers and add it to difficulty settings.