It takes about 1-2 months depending on iteration and feedback. This is from the VERY Beginning to the end, not just the rendering though. So this includes doing a bunch of quick thumbnails till we get the approved pose/scene. That in of itself can take awhile until we settle on the actual image we want to render out.
That time also takes into account that the splash artist has various meetings through out the day and might be helping other splash artists out with paint overs and feedback as well, so its not like 8 hours a day for 1-2 months straight.