on the Vit D thing - I read , last year sometime, that in winter for those north of the equator it takes a bit longer.
if the sun is low in the horizon stay in the sun longer than the 20 minutes.
The farther north the longer you need.

One doc also mentioned no sunglasses as the eyes will absorb it quicker - but of course don't look at the sun directly.
i know you all know that part..

face towards the light so eyes can get the reflected rays- and exposed skin will better absorb also.