From the Overpass QL docs, it looks like I’d use [diff:"2019-09-01T01:00:00Z"] (or whenever I started this project) in my query. I’m having a tough time figuring out where it goes in the query, though.
The closest I’ve come is adding it to the first line: [timeout:900][out:json][diff:"2019-09-01T01:00:00Z"]; in my street query which produced the error “The selected output format does not support the diff or adiff mode.”
It sounds like I’ll need to change more of the query to work with diffs, but I don’t have time to dive into that right now.