Actually, the 4th and 5th degrees are strictly a double degree, worked in the same Ritual.
A 3rd Degree MM from St. J’s Lodge can petition for his initiation in a St. A’s Lodge 9 months after he has been a MM. He gets his 4th/5th degree and then after a period of 12 months for his 6th degree. After his 6th degree, a brother has to wait for 24 months until he can join a Chapter, and he can do nothing to get this moving any earlier, not even a Dispensation!