But how long will that take and how clean would that be?No. I feel the bottom will age just fine without being exposed to light.
I am more so thinking of when purchasing live rock from a lfs. It's not white on the bottom and usually contains alot of different life.What is it that makes you think rock "cures" faster when exposed to the light? I think your premise is just incorrect. If by cure you mean turn greenish/brow then by all means turn it. If by cure you mean colonized with bacteria then no need to turn your rocks.
If some areas have less access to oxygen that may impact the bacteria or type of bacteria that grows...but in that case turning it just kills off some while you "cure" others.
No, one thing I do is every base rock gets a smaller flat rock glued underneath of it so the footprint of the rock is very minimal touching the substrate.
This allows for very linear flow under the rock to carry debris away. I used to rotate until I took this approach. It makes for very cool nooks and overhangs.