How long does it take for a bruise to form?
Bruises will form immediately depending on the nature of impact to the skin. Bruises appear reddish the moment they develop; just as the blood appears under the skin. Visit http://kidshealth.org/teen/your_body/skin_stuff/bruises.html# for more information.
I have light skin- right away. It depends on skin type, age etc. So it varies.