Isn't CC's date updated what you want? That date is reset whenever metadata is sent from calibre to CC.
Or are you talking about the content server display? In that case the options you get are controlled by calibre, not CC. There isn't any standard way to get a list sorted by calibre's last_modified. You can fake it by creating a column built from other columns, setting "sort by date", checking "Show in tag browser", and using the template
Code:
{:'format_date(raw_field('timestamp'), 'yyyy/MM/dd')'}
This will give you a category in the content server sorted by date (ascending). to get to the latest date you must scroll to the bottom.