Some from 30 mins, others a little over an hour. From these I've learned to paint/draw very small as to get the colors down right the first time. As you can see, the last two images at the bottom are the same. I painted the bottom one first, and felt that my colors and values were jumping back and forth too much so I made a new one, zoomed out really small, and just laid down the basic colors and values from the reference.
I've also began to create a blank separate file to be used as a palette so that I could determine beforehand all the skin tone colors and also to compare the values. Before I would just pick a color and lay them on top of the painting and just hope that that the value and temperature works. This turned out to be really erroneous and time-consuming. (NOTE: in Corel Painter, there is a mixer palette, which would be perfect for this, but Photoshop doesn't have that)