I have seen that, in the document, there's only one date to know when was the document updated. But I can't find a date to know when was the content stream updated. That is, I want to know when was the binary updated rather than attributes.
Do you know wich attribute indicates the last modified date of the content stream?
No there's no distinction between the different properties with respect to the auditable props.
You could add a new property that gets updated on content stream close.
You may also be able to abuse the URL of the content stream since by default there is a date element in the URLs of the content store. However not guaranteed to work.