Conditional: current user updated post in the last X days

I just realized that in my previous answer I focused on duplicating your current SQL query but your query is not what your question’s text says.

One condition seems to be that the current user must be the original author.

If the revision history exists, then we would need to find out the who authored the parent post for each revision.

Instead of going down that road, I think you should consider storing that information in the user meta table.

There exists the _last_edit post meta key to determine who last modified each post. This is e.g. used in get_the_modified_author() function.

My suggestion is therefore to store a similar _wpse_last_modified_cpt user meta key with the unix modification time as a value, each time when the cpt is updated.

Then you can fetch it for the current user and check if the stored datetime is within the wanted limit.

I hope I’m understanding the question correctly 😉

Previous Answer:

It sounds like you’re looking for this kind of query:

$query = new WP_Query( 
    [
        'post_type'     => 'cpt',                       // Adjust to your needs!
        'fields'        => 'ids',
        'author'        => get_current_user_id(),
        'post_status'   => 'publish',
        'date_query'    => [
            [
                'after'     => '7 days ago midnight',  // Adjust to your needs!
                'inclusive' => true,
                'column'    => 'post_modified'         
            ]
        ]
    ]
);

that generates this kind of a WHERE part of the SQL:

WHERE 1=1 
    AND ( wp_posts.post_modified >= '2016-09-09 00:00:00' ) 
    AND wp_posts.post_author IN (123) 
    AND wp_posts.post_type="cpt" 
    AND wp_posts.post_status="publish" 

You should then add a is_user_logged_in() check before running the query.

Then you can use e.g. this kind of check:

if( $query->have_posts() )
{
      // Do what you need to do!
}

to see if a custom post, written by the current user, has been updated within the last n days.