Nice! I would personally have composed so that the foreground feature (rock?) was off to one side of centre and maybe "introduced" a few addition small stones going toward it.
Rather than wait for the light to get low enough, I use ND (neutral density) filters of varying degrees of darkness. Square ones are the best bet, cheaper than ones to fit specific lenses if you have two or three different filter sizes. They can be used with a holder, several filters at the same time or just held in front of the lens.