Granted that the orbital time decreased due to the impact, but would orbital time also decrease because of the now lighter mass of the asteroid (ejecta loss)?
Good question.
I think that the loss of mass would cause the ORBIT of the asteroid to INCREASE in diameter, since the pull of gravity from its host would be lessened, therefore it’s orbital period would increase.
But the kinetic energy of the impact cause the orbital period to decrease, so it offset the mass loss tendency to increase.
The impact apparently was more like a ball on a roulette wheel being spun by the croupier.................