Do not wash your hair the day you intend to do the colouring. Experts recommend that you wait 24 to 48 hours after washing the hair before applying hair dye. Freshly washed hair is devoid of fat, which helps to facilitate absorption of hair dye.
The usual developing time of hair dye is 30 minutes and it ensures saturated colour result. For lighter shades and in case of stubborn grey hairs, you may extend the time up to 45 minutes in order to obtain more intense colour and even hair coverage.