Yes all of 4th year is scheduled by YOU. VSAS, Clinician Nexus, random physicians you find that are willing to take you on, etc.
Even the 4th years that have the Florida site as their core site have to apply through clinician nexus for their 4th year rotations. You get no help from the school at all. Just a big Guidelines packet they will refer you to anytime you have a question. (i.e the last time I asked a question, the response was something like "you can find your answer in the Guidelines, page xx" with no additional input)
You can probably start planning it around the time people plan 4th year rotations in general. January is a good starting point (on the early side). Some places dont really start until March or even later