Afternoon wedding attire should be proper and polished, falling somewhere between weekend casual and black-tie optional. While a before-sunset ceremony is less dressy than an evening affair, most daytime weddings are still semiformal, which is generally defined as a dress for gals and a suit for guys.
Women can rock a number of looks appropriate for semiformal afternoon weddings, from a classic dress to separates.
Just because the couple says "I do" before the sun sets doesn't mean you get to leave the suit and tie at home. Men should still wear a suit for afternoon weddings. Choose a dark suit and a conservative tie for any type of late afternoon wedding, unless the invitation specifies a black tie event. Then dust off your tuxedo or hit the rental store.
Never wear a tuxedo to a wedding unless the invitation specifically states that it's a black tie event.
How Formal Is The Wedding?
Re-read the invitation, paying careful attention to the formality of the card stock, engraving or calligraphy. Typically, the more formal the invitation is, the more formal the wedding is.
Note the ceremony and reception locations. These are also clues to the formality level. A ceremony and reception at someone's home is either informal or semi-formal, but a late afternoon affair at a church and exclusive club is likely dressier.
Wear a short cocktail dress or dressy suit for an informal or semi-formal late afternoon wedding. For a formal late afternoon wedding, wear a dressy cocktail dress or a less formal long dress.
If you wear a strapless dress or one with spaghetti straps or a deep neck line, bring a cover-up, particularly if it's a religious wedding. Too much skin in a house of worship is not appropriate.
Wearing a black cocktail dress to a late afternoon wedding is perfectly acceptable and, in fact, is a good safe bet when you're not sure what to wear.
Don't wear white to a wedding. You don't want to compete with the bride.