Here's a tutorial showing you how to setup GBTimelapse AutoRamp to do a Sunset time-lapse using a single 9-stop neutral density filter.
... and here's the resulting video, captured using a 5D Mark III with 16-35 mm lens. The Milky Way was brilliant that night.
Pros & Cons of the 5D Mark IIIA major advantage of the 5D Mark III is the ISO 50 setting. It allows you to use a one second bulb time at f/2.8 with a 9-stop filter during daylight.
However there are two minor disadvantages to the Mark III. First, the Depth-of-field Preview button has been moved to the other side of the lens from the Lens Release button making it awkward to do the lens-twist procedure. Second, unlike the Mark II it's not possible for GBTimelapse to change the AEMode - you must do it manually on the camera Mode Dial.