Seller usually vacate the property by the time the buyer takes possession. This is usually close of escrow plus two to three days.
This should been made clear to them by their agent.
Kawain Payne, Realtor
You will find the answer to this question on page 1 of 8, section #3 closing & occupancy, sub-section B seller occupied or vacant property of the California Residential Purchase Agreement. Unless there were counter offers made that made specific changes to this section of the purchase agreement. Your agent should be able to clarify this very quickly. Good luck!