Took about an hour and half to finish, following(and improvising) the tutorial by Kent Trammell. +skipping couple steps due to several crashes. Could only render it at 1152x648 resolution. But the render times weren't that bad. 18min max. 500 samples
You can find his tutorial from https://cgcookie.com/blender/2013/11/26/creating-antelope-canyon/
