As indicated, the level skip does not work on the flying level, but it works on every level before and after that. If you want to speedrun the gallery, just open the game folder after launching it at least once, open the "cg" file, and below the line where it says [cg] just enter "roomx=1", where x is each number from 1-55 (each entry should have its own row). Save the file (maybe copy it first) and voila. I ended up with every CG except for one of the tentacle ones (it was replaced with the succubus defeat scene). Also ensure there are no duplicate entries.