As far as I know CHC takes like 10 weeks for Pakistan. In this case, I don't think they're bound to reply before September session. Because if they were bound to reply before classes begin, people will submit their file whenever they, want ignoring the processing time provided by the CIC. They surely will try but if they've some doubt, then they will take their time. In most cases, your university will let you start in the January session though. Anyway, almost 9 weeks will be ovsf by August end, so you shouldn't worry. If they think you're case is genuine then they will give visa for September session.