so you see your portal directory under portalname.esri.com/arcgis/sharing.
login under that directory to the account with the service item and go to user content.
find that item and click on it which will open up the user item.
At the bottom of that page you will see Update Item. Click on that link.
Then follow step nine where you replace the current text with the text that is in step 9 and click the Update Item button.
Once you have completed those steps under the directory you can go back to the portal site portalname.esri.com/arcgis (no sharing) and login with the account you were editing the item info on. Then you can add it to a map save the map and under the map details you can edit the tracking intervals.
Let me know if this works for you
Russ