Personally, I think that this detail is important less for accuracy to modern tropes, and more to inspire fear into players who know those tropes. That moment when players point out that he's standing there in the "sunlight", in the middle of the day, gives way to one of those nefarious DM smiles, and the classic, "Oh, I know! Isn't it great?".
The other reason that I feel this is important, is because Strahd should be ever-present in the players' minds, and that he should show up from time to time to taunt the players as necessary. He's supposed to pop up when he's least expected, right when it most terrifies or otherwise impacts the players. A patron in the toymaker's shop, a coy finger-wave from outside the inn, a sudden appearance and compliment on the spell cast by a player in combat, a comment to the players after they meet a madman that his man is his (Strahd's) finest work, or a sit-down dinner with the abbot, followed by an early-evening stroll around the grounds - any of these kinds of moments can help to establish Strahd as an ever-present force, reminding the players why they're there. Restricting these to only night-time Strahdian escapades can limit his presence, since most players are smart enough not to venture out at night.