Standard time is 120 hours=5 days. The trait "High Libido", good physical shape (athletics skill) and sexperience reduce it. I don't know the exact formula though.
You can use the blue pills to speed up the process, however according to the Wiki this will increase every further re-eggplanting, if you do it too often by very large amounts (exponential growth).
Larger penis has higher impregnation chances, small penis lower. Also the graphics change if that's what you're interested in. Finally, yes, some girls react to penis size by giving a few extra LP when first seeing it (most react positive to a large one, but some prefer it small). That is negligible in the whole picture though. But there is only a minimum amount of "cheating" (depending a bit on your definition) in the game anyway and it doesn't depend on your penis size.
You can get them to become your girlfriend or sex slave through gameplay. However, this is by playing, there is no "status switch" as such in game, you need to go through their stories.
(Theoretically you can change some variables in the save game or through the console, but I wouldn't know which, and it will mess up your save with 99% certainty so you cannot continue playing after that.)