From San Carlos Island to the Anchorage at Garden Key in the Tortugas is about 121 miles. With any wind you should be able to manage 4.5 to 5 knots in your Cal so, for all intents and purposes its about a 21-25 hour sail although will likely take you longer given the propensity for squalls off the Everglades once the sun goes down. If you know how to handle the boat, the squalls can really give you a sleighride, if not...well, that depends upon you. I'd be careful about locking myself into a schedule. To get an idea what average weather conditions are like pull up the coast pilots but generally in the winter you're looking at series of cold fronts that bring very unpleasant (cold!) north westerlies. I'd go by November or delay until May.
You can get quite a bit of information from ActiveCaptain.com
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