White shirt worn with blazer and greys at night :
Should not be wearing black shoes with a blazer
White shirt usually demands black shoes
Black shoes after 6PM
Which shoes to wear? Do the latter two considerations take precedence?
A white shirt worn at night with a blazer is less likely to be a BD (or at least more likely to be a spread collar), so mink suede seems less a less appropriate substitute , and that's before we get back to the fact that it's after 6PM and mink suede would be inappropriate anyway.
I think the rule you stated above really applies to business wear, not evening wear. The idea is that black shoes are generally only worn with formal business attire during the day, and a blazer is not formal. At night, outside of the business world, things are different. I would go with the black shoes. You may find this thread interesting: http://www.styleforum.net/t/309735/black-tie-casual