The water parade is right after the Wishes fireworks (at least it was last year when we stayed at the Poly). On multiple nights, we would watch the fireworks, then within about 5 minutes, the water pagent started.
I think the fireworks were at 9pm then the water pagent right after.
It was January, so things were a bit earlier than they may be now.
Was it worth it? If you plan on watching fireworks as well, then sure....if not, then it wasn't anything I would stay up extremely late for, or plan around.