How long does it take for new images to appear on social media preview once updated?

Branch will update the link 'og' parameters immediately after it is updated. However how the social media descriptors show up on a platform are controlled by the platform. Different platforms handle these links in different ways, the platform might scrape the link everytime it is shared and the image might get refreshed immediately. However in most cases the link is not scraped regularly hence you might see a time lag before the image is updated for the link. If you are sharing on Facebook owned platforms you can manually scrape the link by visiting https://developers.facebook.com/tools/debug/