I take generally around 20-40 mins depending on how detailed the work is. Tips for me that work well
-I always do a face chart the day before.
-I moisturizer the crap out of my models so reguardless of the person... her skin stays soft.
-I bring white, red, pink & yellow foundation mixers with me so I can mix shades quickly.
-I carry a laminated list of foundation swatches with me so I can hold it up to the models face and get a better idea of what is going to match her before I put anything on her.
-I try to work with as many products that are famlar to me as possible so I learn how they react to different skin types.
That's all I can think of for now... but I have been told I am quick... even when I face/body paint... so I hope that helps!