It is the UV B light from the sun that create vitamin D.

This spectrum is filtered out by the atmosphere. It is also filtered by glass.

So, you will not get vitamin D sitting by a window.

I understand that it is generally best to catch rays at noon because the rays from the sun pass through less atmosphere and should be higher in UV B radiation.

Morning and evening are bad times because the sun's rays have to pass through more atmosphere.

One only needs about ten minutes of sun; so I've been going out at noon on days with low cloud cover.