It is best to wait at least 4 weeks in between dyeing a person's hair, but those people with weaker hair should wait at least 6 or 7 weeks in between dye jobs. For those people who want to make sure that their hair will not be damaged in any way, it is best to wait a minimum of 6 weeks to ensure that there will not be any damage.
The state of the person's hair after the coloring dye treatment is what should determine whether or not they fix it immediately or wait. If the hair was damaged in the dye job, then it is crucial that the hair is fixed before the color is fixed. The hair will need deep conditioning treatments every few days in order to recover from the dye job damage.
Another thing to keep in mind is the color that the hair was dyed. It is always easier on hair when it is dyed darker so those who are coloring their hair darker colors will be able to head back to the salon much sooner than those people who are dyeing their hair lighter. Another option is to try to do a dye on just the regrowth or the roots rather than dyeing the entire body of hair.