The initial symptoms of rabies are mild, but they quickly become serious. The incubation period is the time it takes for symptoms to develop after a person is infected with the virus.The incubation period for rabies is usually two to 12 weeks, although it can be as short as four days. It is unusual for the incubation period to last for more than a year.he incubation period for rabies is usually two to 12 weeks, although it can be as short as four days. It is unusual for the incubation period to last for more than a year.