Kuki, read the original post. The ship will just be in port 0700-1200. Given it takes a few mintues to get off, and you are usually requested to be onboard some minutes before leaving, taking a 4-5 hour private tour is really pushing the envelope.
With that short of time, I would either opt for a private tour that you can control your speed and plan on being back by 1100 or actually take a ship's excursion. Me, I would take the ships excursion to the Terrace Houses.