Meta entry header — what should I add?

Does anyone have a good idea of how I could revise this code to only show \[post\_modified\_date\] if it’s greater than 30 days (for example) after \[post\_date\]?
Thank you! This has been giving me headaches for days 🙃

//\* Customize the entry meta in the entry header
add\_filter( ‘genesis\_post\_info’, ‘sp\_post\_info\_filter’ );
function sp\_post\_info\_filter($post\_info) {
$post\_info = ‘Published on \[post\_date\], Last Updated on \[post\_modified\_date\]’;
return $post\_info;
}