Hi there,
This feature is currently in beta as outlined here. I am not aware of a timeline for this feature to go live to all of our customers, however, our Prodcut team has moved to the planning stage on how/when they will enable this. You will receive a product notification in your HubSpot portal when the feature is available for use within the HubSpot social publishing tool.
All the best,
Rachel Appleman
HubSpot Customer Support