I don't know much about this, except that blue light at night supposedly might interfere with your circadian rhythms.  Red light doesn't, and I suspect it is because we evolved with fire... if looking at a fire reset our circadian rhythms that would have messed us up quite a lot.

I doubt looking at the sun at dusk/dawn improves eyesight. It certainly causes your pupil to shrink way down, which focuses things better, and so it may appear to immediately improve vision, but that isn't fixing anything permanently.  But there might be more to it, I'm just not aware of it.