This is easy. Date & time display should be controlled under Settings –> General, using whatever date/time settings you’ve configured for your broader WP install. So when you change it to the third time format option, this will be reflected in your forms.
Yeah that looks fine and those settings work for me in my dev environment… Have you tried clearing your permalinks by visiting Settings > Permalinks and/or deactivating plugins to see if there’s maybe a conflict?