As long as their are no chemicals (such as bleach) in your hair dye, then you can't dye your hair too much. A brand I know, that doesn't have any chemicals in the hair dye, is Manic Panic.
Yes, you can dye your hair after using Sun In a long time ago. It will not hurt your hair at all.
about 2 weeks
As long as you dont get your hair wet -_-
Yes it will dye your hair black(depending on how long you leave it in). I is great if you want a brunet hair color. just dont leave the coffee in your hair as long
about 6 weeks
You should wait at least a month to dye your hair after surgery.
Pretty long
You should never dye hair that has just been cleaned as this can lead to damage. It is best to wait round 24 hours. During that time try not to use any hair products and try not to apply heat to the hair via hair drying or tongs. I often wash my hair in the morning and dye it later that evening and this seems to be long enough. It is half the recommended time but it is long enough for natural grease build up. Always read the instructions - you will find this answer within them.
can i use hair dye if its already open and its been 24 hours
a hair dryer does not dye hair
Depending on what type of hair dye and what chemicals are in it. I have been dying my hair since middle school and then i started using permenant dye after that. I stopped 6 months ago and it still hasn't washed out. So with that being said becareful with dark permanent colors.