Once your home is listed for sale or for rent by your agent, they retain editing control while the listing is active.
If your home is listed for sale by your agent on Zillow, your agent will need to make updates to your listing. If they have posted your home for sale using their free Zillow profile, they will be able to make changes to your listing by logging into their Zillow profile and making the changes there. Those changes appear live on Zillow as soon as they have been made.
If your listing is being provided by a listing feed, the agent will need to update the listing at the source. Listing updates can often appear on Zillow within 24 hours, but can take as long as 48 hours.