This was previously (recently) listed as a bug (BUG-000183270), but it has since been marked as resolved. After the resolution was implemented, the expected wait time between an event occurrence and a webhook firing has been stated by ESRI to be 1 to 3 minutes. In most other applications that I work with, webhooks are sent near-instantaneously (you can see them hit the webhook receiver application like 1 second after the event occurs).
https://community.esri.com/t5/arcgis-online-questions/how-reliable-are-arcgis-online-webhooks/m-p/16...
1 to 3 minutes for an enterprise cloud application to generate/fire a webhook payload does not seem viable to me.
