A formal wedding during the day would have men in morning suits or cutaways. Strictly speaking a tuxedo shouldn't be worn in the afternoon. Formal could also mean white tie.
I think the real question we need to ask ourselves is how any of our young people are supposed to be able to afford a tux. Many twenty-somethings, even those who invested in some of the best educations in the country from Harvard, Yale, Princeton, (nice try Stanford, but you're West Coast), are finding absolutely no jobs are available for them. Despite all the boasting about the recovery, it's hard to buy a tux, when you graduated 1st in your class with a PhD in South Pacific Aboriginal Tarp Batiquing and NO ONE will hire you.