There’s a new version of the plugin out that uses the site’s Time Format (on the Settings page) to determine how to display the time.
Note that the plugin uses transients to reduce the number of times the ICS file gets loaded, so you may need to force a reload by adding reload=”1″ into your shortcode. (Be sure to remove it when you no longer need it, as it will make the page reload the ICS file from the remote source on each page load.)