Between 12 and 16 is the best time regarding sea breeze, but this is rare as we have typically much more wind here.
But if the wind (in theory) were constant all day, and you had vacation or weekend - we would definitely go out at the same period, between 12 and 16
Because it is warmer, and your body is most "fit" at that time of the day.
Especially at wintertime, there is really no discussion - you can ONLY go out between 12 and 15 because it is freezing too much before noon, and it gets dark after 15
In the summer we can get many hours - as there is light from 4 in the morning till 23 in the evening, so you have almost 20 hours you can go kiting every day
(okay, up in Norway they got 24 hours light - so even better)
But even in the summer, it is most pleasant to be out early afternoon when it is okay warm and you dont need a thick suit
So up here in the Northern hemisphere in Scandinavia the UV problem is not an issue - other more important factors dominate
Noone wears sunglasses on the water here - it is stories from other countries
So no - sun is not a problem at all here, but when travelling to warmer locations closer to the equator you dont wanna be out too much from 12 to 16, but before and after - AND wear sunglasses on land