Hair can be dyed two days in a row, but it is best to wait at least 48 hours before the second application according to Good Housekeeping. Immediately applying more chemicals to hair just damaged by chemicals can cause extensive damage to the hair that far exceeds the acceptable degree of damage for colored hair.
If there are problems with the initial appearance of the applied hair color, it is best to call the number on the bottom of the box before taking action. The color expert may have suggestions to save time, money and damage to the hair. If changing the color is the only option, condition the hair well before dyeing it again to at least minimize the damage.