That's when they start yeah, so they will be advertised earlier than this, I've seen them starting from April for Sept/Oct starts, but I've also seen a load recently for Sept/Oct starts, so I think it depends on when the supervisors get around to advertising the position.
For example, I've seen a teaching fellowship that I want to apply for, job ad ends 31st of July, job starts 1st of Sept - so not exactly much time to interview and for people to give notice to their employer!
I would advise you to keep looking - sign up to the job alters on jobs.ac.uk. There's still plenty about.