Is it useful to track dev time with CI/CD? Estimating is hard, but it is made easier with good record keeping.
Is there a known solution to tracking dev time on a ticket by making use of CI/CD to update JIRA tickets or the like with logged worked time, based on the time difference between first commit and final CD?
You can use the rich jira rest API for this kind of automation work. Jira API provides mechanism to update logged hours using PUT /rest/api/2/issue/{issueIdOrKey}/worklog/{id}

You can use this rest API endpoint to update the corresponding issue with the difference of first commit timestamp and first successful CD.

Find more about it here.