What we called concept art often is not. Literally, concepts are for technical use. It can be for realize a 3d model or just to illustrate a specific mood for a scene, but it has to absolve a task and not only for entertainment. Concept arts that are made for illustrate, captivate attention or show the aesthetic side of the product are properly called promo art.
Forged Chaos studios commissioned to me a figure in leather armor as promo art for their in the making game Trials of Ascension. And after some references with real historical armour and inspired by Skyrim concepts, I painted my own. It took me 1 hour the B/W and other 5 for colors and finalization. That’s too much, so my task for next month will be focused on encrease my speed especially in the second part of the work. Are you wondering how? Draw, paint, draw, paint, draw, paint and then… Again.