Turnaround is roughly three weeks. Backgrounds are very minimal or nonexistant. There is no approval stage for any of these - changes will only be made if a detail or marking is missed when clearly shown in the reference or description given.
How are Bronze sketches different from Silver sketches? Bronze sketches are quicker, messier, and less detailed. If you have a character with complicated, precise markings, I will be turning you down for Bronze sketches and recommend you choose the Silver option in order to do your detailed character justice. (A leopard or a tiger would be fine; a character with an exact number of spots, stripes and tribal tattoos would not be doable under the Bronze timeframe.) On the plus side, it becomes very affordable to pay a small amount of money and get three poses of your character doing a variety of things, or if you had two characters, two "frames" of them spending some quality time together in two different poses.