Show modified posts only

I’m trying to use this plug-in to show new or modified posts within the last 45 days. It does a great job if I remember to change the post date. Is there any way to grab the posts based on the modified date only?

Here’s the code I am using:
[catlist post_type=”page” show_protected=yes thumbnail=yes thumbnail_class=alignleft excerpt=no after=’-45 days’ post_parent=’196′ order_by=modified date_modified=yes]

The page I need help with: [log in to see the link]