During the day at home, ladies could be as informal as they wished – they had their pick of comfy lounging pajamas or morning dresses (often wrap style), skirts and sweaters, housedresses, slacks and blouse or sweater, etc., depending on what they had going on. But choosing day wear for street wear was another matter. There were several factors to consider, including location (country vs. town), season, and activity (shopping, school, office, etc.). Above: daywear outfits, McCall's, 1932. 
Fall frocks for day, 1934
Designing Women: The Art, Technique and Cost of Being Beautiful by Margaretta Byers (1938) notes that the afternoon dress is “a vanishing American custom….You can wear a suit or tailored dress nowadays from breakfast to cocktails, and through cocktails too, unless it’s a real party. Of course, if you have an important lunch date, you will wear your nicest blouse with your suit and furs instead of a scarf. And you’ll wear your pet hat. But that’s as far as you need go.”
Charm and Personality by Marianne Meade published the same year, echoes this. “Informal day clothes are suitable for all the usual daytime occasions – street, shopping, school or office.” A well-chosen morning costume could “be made to serve for even the most formal afternoon occasions” including a formal tea or reception, a formal wedding, or a cocktail party. On such occasions, the author notes, “you may wish to dress up your morning costume with a more formal blouse or accessories, or perhaps a fur neckpiece, but these additions are not actually necessary.”
Suits, Delineator January 1935. Left: tweed suit with double-breasted jacket. Middle: Tunic dress. Right: Coat without fur. When you want to look more formal, add a fur cape or scarf.
Charm and Personality goes on to say: "In this group are tailored suits or dresses, very simple afternoon dresses, and semi-sport dresses of the spectator type. With these you should wear hats simple in design and sparingly trimmed. Coats may be of the sport or semi-dress type; of fur, cloth, or a combination of the two. With the afternoon dress and semi-dress coat you may wear plain dark pumps with medium high heels. With tailored clothes, low heeled oxfords or sturdy pumps with medium high heels are appropriate. Gloves should be plain and either tailored or sporty, depending on the rest of the outfit. The purse should be appropriate as to design and fabric. Avoid dressy purses of silk, velvet, or suede with elaborate clasps, handles, etc., except for afternoon wear. Little jewelry should be worn and that must be simple and of a sporty rather than dressy type. Perfume for morning wear should not be heavy."
Good daywear accessories. Vogue 1938.
"The entire ensemble should be of conservative color and simple design. It should have very little trimming, and the material should not be “dressy.” Must be of the “sporty” varieties, such as soft woolen, serge, tweed (not too rough), knitted fabrics, etc."
Some daywear fabrics, Vogue 1936.
Designing Women also touched on this: “However, you must understand that there are suits and suits. Swagger suits belong in the country and are worn with sweaters and fedora hats. Usually they are rough or monotone tweeds. But we can’t say all tweeds belong in the country. Because there are lovely soft Lintons and lacy tweeds that lend themselves to tailleur and dressmaker styles and go quite elegantly to formal luncheons.”
"Swagger" suit for country, 1941 - characterized by the full back and loose front.
Above: A tailored daytime suit with appropriate accessories, 1936. Below: Two daytime frocks for fall, Ladies Home Journal November 1931. The red one-piece dress is of wool. "Note the interesting two-pointed effect at the elbow." On the right is a street dress of wool crepe by Paquin with wide revers and deep cuffs of silk piqué.
One point that all period etiquette and fashion advice books we’ve read agree on is: better to be underdressed than overdressed. So, what about a vintage event that starts in the morning and goes through the afternoon with no practical opportunity to change? If a gal wants to follow the “correct” dress conventions of the era, she’d dress for morning rather than afternoon, since morning clothes can carry her smartly through the entire day, whereas in afternoon attire she’d be overdressed for the morning.
Above: Chic streetwear, McCall's March 1932.
