24-48 hours
3 weeks or more is best
I recommend waiting at least 2 weeks, but it is very damaging to hair to put more than one chemical process on it.
long hair
If you already have dyed your hair a dark color you need to bleach it out, your hair should turn a blonde yellow color, then bleach it again. Then buy a white hair dye. Then leave that dye in your hair for a good 45 minutes. Then your done! I wouldn't suggest dying your hair again for a very long time because this can be very damaging. And this will work much better if your hair is its natural color.
no, it won't bleach your hair but it will dry it out!
You can highlight you hair any time, as long as you hair is healthy and not damages by previous colorations or from bleach. If that's the case, wait until your hair is healthy enough and use hair treatments or cut your hair.
It is practically impossible. You have to have roots to bleach your hair and root on hair of at least a inch or more to safely bleach them. You don't want bleach directly on your scalp.
3hours
When you bleach your hair, you are stripping all the colour out of it. There's no way for the color to come back in, therefore, it will last forever. (or atleast until you cut it off.)
Usually, any time after. But you should check the dye and bleach boxes just incase. If you can bleach your hair after, just make sure your hair can handle all of the chemicals.
When you bleach your hair, you are stripping all color pigment from your hair. You will need to wait for new hair to grow back for your hair to return to normal.
It will not hurt as long as it is on the hair. You should not touch the scalp or your hands with it as it will burn and you should never use household bleach because your hair will dissolve in it.