At the moment Triggre can’t do that automatically for you.
What I often do when I want to keep track of when something was created (or updated) is just enter the current date where I use a flow part. Imagine I have a form where users can add new orders. After the form I would use the standard Create Order flow part (which was automatically provided and takes all properties from the Order data item as input). For most inputs I would fill in data from the form. For a “Created on”-property I would fill in the current date and time, which is always available. That would save me creating an automation flow, but it does mean that I need to do that in all place that I use the flow part. Which options is easiest depends on your case.