The Service Dress Blue Uniform is worn (note that this entire paragraph is based on the ALARACT Message and that the Army is still rewriting AR 670-1):

• Year-round
• As an optional dress uniform (currently) when worn with the white shirt and black bow tie
• As a replacement for the Army Green Service Uniform in its Class A and B forms

The Dress Blue Uniform is worn (currently detailed by AR 670-1):

• As an optional uniform (it is mandatory for active-duty officers)
• Year-round
• As the equivalent of a civilian tuxedo when worn with black bow tie (after retreat)
• As an informal dress uniform when worn with a black 4-in-hand tie
• On duty as prescribed by the local commander
• For social functions of a general or official nature, before or after retreat
• On other appropriate occasions. Examples include:
• Funerals
• Memorial services
• Weddings
• Inaugurals
• Parades on national or state holidays
• Parades or ceremonies in which a United States military unit of any component is taking part
• Other occasions of ceremony

While AR670-1 states that the black bow tie is worn only after retreat, in practice Soldiers wear the black bow tie during very formal afternoon events, such as weddings, especially when the event extends into the evening hours.