public void Validate(Appointment appointment, Vet optionalVet)
        {
            string errors         = "";
            int    startingHour   = int.Parse(optionalVet.getStartingHour());
            int    startingMinute = int.Parse(optionalVet.getStartingMinute());
            int    endingHour     = int.Parse(optionalVet.getEndingHour());

            if (appointment.Date.Hour < startingHour ||
                (appointment.Date.Hour == startingHour && appointment.Date.Minute < startingMinute) ||
                appointment.Date.Hour >= endingHour)
            {
                errors += "Choose an hour that is in the schedule of the choosen vet!\n";
            }

            if (errors.Length > 0)
            {
                throw new ValidationException(errors);
            }
        }