I currently have an app (node.js) running in Heroku, using Heroku Connect to connect to Salesforce to read/write data.
Heroku Connect essentially has a copy of selected data from Salesforce, which is pulled in via the Streaming API.
My application instantly writes to the HC PostgreSQL database, which instantly writes up to Salesforce.
This adds a unique reference field that is also instantly generated in Salesforce, however there is delay in this information being fed back to Heroku Connect.
I'm not sure if the delay is because of the streaming API or Heroku Connect, but I'm not sure how to minimise/remove this delay so that Heroku Connect instantly updates with the newly generated field.
Please take a look at the diagram below showing what is instant and where the delay is happening: