Yes I have tried but nothing changes.
I am based in Venice (Italia) and when I take a look on the weather and daylight duration in other places, all the timing are correct.
For example in Reykjavik, Iceland, the sunlight duration in these days is about 4 hours per day, that's correct.
But if I look for locations well above the arctic circle (for example Svalbard Islands) where in this period the sunlight is ZERO hours per days (continuous night) the values displayed from iPhone weather app are completely erratic, generally showing 22 or 23 hours of light!