BE VERY CAREFUL!! I have ten years experience in hairdressing, if you leave the bleach on for too long your hair could literally melt and it would stretch and be chewing-gum like and fall out!!
Bleach is not like any other hair dye as a hair dye stops working after 45minutes so it doesn't matter how long you leave that on for it will stop where as bleach wont it can also send your hair brittle.
May I ask what color your hair is at the moment? As if your a dark color it will go a ginger color or a copper toned color and you will have to use a toner as well as bleach to achieve blonde, also I would not use a boxed-bleach that you buy from a supermarket because the peroxide level is only 9% and that may not be high enough to lift your hair, leaving you ginger.
Do you have a Sally's wholesalers near you?
As I know they will serve any one professional bleach or peroxide without you being a professional.
If you let me know your hair color at the moment I would be more than happy to advise you on the right care for your hair x
it depends on what colour your hair is to begin with
and what the instructions say
some say leave them in for half an hour, some say 40 minutes, ect
so read the intructions
also the less time its on your hair, the less damage it will do
Psy's mother kept bleach in her hair for fifteen minutes.
Though, she is usually a natural blonde. >.>
Psy would assume that it would be longer for darker hair. Hope that helps!
-Psyrenity.Will bleached hair turn green if you dye over it?