Preparing minced garlic the night before using them
It's safe to chop your garlic the night before. It will change color slightly due to oxidation, probably not enough to affect the look of the dish. It will lose flavor overnight though, so I wouldn't chop it until I'm ready to use it. 

Generally the big pain with garlic is not the chopping but the peeling, you could peel it the night before and then chop it just before using without impacting the color or flavor. That's the way I'd go.