The undyed has been sunning itself on my spare bedroom windowsill since about May. It has darkened somewhat but not as much as I expected. Sweden has sun almost 24 hours a day during summer, but it does not get very hot, so maybe heat would have made a difference. I think the hottest it was this summer was 29°C/84°F.
The leather did not dry out at all. This may have been because it was already well-handled and moisturised by my hands. I did not treat it.
I have used this red LV binder for a few weeks now and it has softened up so nicely. This leather is stiff to start out with but now it has become really smooshy and wraps round the contents like a hug.
I did not expect it to soften and I am glad it did because they always feel more like they belong to you when they start to change.