When is It Safe to Put Makeup on Chin Augmentation Scar?

First, you should consult your physician about their personal opinion on this subject. Us surgeons are very particular about how we and our patients take care of scars. In my opinion, most scars are closed and can be covered as early as the day after the stitches are removed. The key indication is when there is no more bleeding, oozing or crusting. If nothing is coming out, nothing should get in.
If you or your surgeon is reluctant to use cover that early, how about a band-aid and tell people you fell and hit your chin? Half the world has scars under their chins from falls.

Usually cosmetics can be used on surgical incisions 48 hours after suture removal. This assumes there is complete healing and no gaps or area of crusting on the incision. If crusting is still present, then you can apply around the area of crust, but not directly on it.
Once healing is complete, if the scar is raised or red, certain creams can be useful. As your doctor which ones he or she recommends. I am partial to kelocote for hypertrophic or thick scars. Mederma, scar guard are also both reasonable alternatives. If redness is present at more than 6 weeks, then steroid cream can sometimes help, but steroid injections or certain laser treatments may be better.
Hope this helps and best of luck