chao growth

This isn't exactly correct. Chaos take 3 hours for their first evolution, and I believe 7-8 hours after that for their second. This is actual time spent IN the garden. Petting your chao with a dark character (Shadow, Rouge, Eggman) will cause your chao to turn darker, if and only if that chao is a normal (non colored egg) chao. If they are a colored egg chao, they will simply turn dark. (Grow a spade tail and pointed head, eventually evolving into a dark chao) Same goes for hero chao. Pet your chao with a hero character, and if the chao is non-colored, it will begin to turn white (Often with blue arms/feet/head extension things and a yellow belly)

No matter how you raise your chao, there is no way to fast forward it without hacks (Action Replay might have a code for it, but I have yet to find one)

I suggest leaving it on for a few hours while you're able to keep an eye on it here and there and wait for them to evolve. :P But keep in mind! Your other chao will evolve as well, or possibly die depending on their age. If they're happy enough, they will reincarnate. If not, you will never get that chao back. So when you're about to wait your time out, be sure you're okay with letting your other chao age and evolve as well.