To me, the optimal is sailing around for the first ~10 or so turns, enough to virtually finish Code of Laws. Hopefully you find a city-state or two, and find a solid enough city location. Anything more than that and I feel you're behind the radar, but anything less than that I don't think is as optimal in terms banking the pre-settling bonus.
The "tough" part will be whether to find a location and park the settler, or keep exploring around and come back to the spot. And obviously a big bonus if you can find a natural wonder to give you some big tile yields for that first city or not.