McDonald’s is rolling out all-day breakfast at every restaurant in the country. But can the boost in all-day McMuffin sales help the burger chain’s stagnant sales? (Pamela Kirkland/The Washington Post)

It was lunchtime at the McDonald’s at 17th and Corcoran streets in Northwest Washington. But if you looked at the giant promotional cardboard clock in the center of the store, where the numbers had been replaced by the 12 items on the chain’s long-awaited all-day breakfast menu, it was a quarter past Sausage McMuffin With Egg. Or, for those who aren’t breakfast people, 1:15 p.m.

Shelby Fullen, 25, is a breakfast person. Especially a McDonald’s breakfast person: “I’ve only gone to McDonald’s for the breakfast,” she said.

Incongruously, she’s also a yoga person, flopping her rolled-up mat onto a table while she waited for her order — a yogurt parfait and an order of hash browns (“Always the hash browns. Sometimes the pancakes.”) — on her day off from work as an anesthesiologist’s assistant at Washington Hospital Center.

“It’s a little contradictory,” she acknowledged. If people in her yoga class were to see her, “they would laugh.” But she didn’t care. “It’s worth it for McDonald’s.”

Until Tuesday, Fullen and other fans of the Egg McMuffin, sausage biscuits and other breakfast foods could typically order those items only from hot cakes o’clock until half-past sausage burrito — you know, 4 a.m. to 10:30 a.m. Breakfast items are cooked on lower-temperature griddles than burgers, and the company didn’t want to sacrifice valuable grill space. But bowing to market pressure from fresher fast-casual alternatives such as Chipotle and Panera Bread, as well as to an overall trend toward more healthful eating, the fast-food giant realized that it needed to give its dwindling customer base what it wants: McMuffins around the clock, hypertension be damned.

Egg McMuffins are a menu item that customers can get all day long at McDonald’s. (Tonya Wise/Invision/AP)

Well, not everyone’s getting what they want. The new breakfast menu is a limited selection of the most popular offerings, so some items, such as the McGriddle sandwich, a McMuffin-hot-cake hybrid science project, or the Big Breakfast, a combo platter of hash browns, scrambled eggs, sausage and a biscuit, were left behind. And some, such as the biscuits, were available all day only at certain McDonald’s outlets, primarily in the South.

“I thought it was going to be all the breakfast,” said Nadia Johnson, 31, who had stopped into the store at 14th and U streets hoping for a Big Breakfast. “I have no groceries” at home, she said. She ordered the hot cakes and sausage and a McMuffin instead. It was 11:15 a.m., well past traditional McDonald’s breakfast hours, but still early enough in her opinion.

“I try to keep breakfast breakfast and dinner dinner,” she said.

Something about the meal, or maybe the intrinsic predictability of fast food, inspired such repetition.

“Breakfast is breakfast,” shrugged 26-year-old Rick Gonzalez, who works security for the Lincoln Theatre and the 9:30 Club, as he claimed his Sausage McMuffin With Egg and hash browns.

“It’s not lunch lunch,” said a woman tucking into a plate of hot cakes around 2 p.m. at the McDonald’s at 1916 M St. NW, before declining to give her name or elaborate any further. (She was one of the few. The hot cakes weren’t exactly selling like, well, hot cakes.)

A philosophical question: What makes breakfast breakfast? Is it the time of day you eat it or the presence of certain ingredients, such as eggs, bacon and syrup? McDonald’s breakfast-eaters were split on the answer.

Breakfast in the afternoon: “Not breakfast,” was the ruling from Julien S., 24, who stopped into the Dupont outlet for a Sausage McMuffin With Egg around noon before heading to his job as a server at a 14th Street restaurant.

On the other hand, Arissa Morrell, a 21-year-old international affairs student at George Washington University, declared breakfast “the best meal of the day,” no matter what time you eat it. She was waiting for her Sausage McMuffin With Egg at the M Street McDonald’s, where she had dropped in on her way to a friend’s apartment.

“I really came out of my way to come here,” she said — four whole blocks! — even though she hadn’t come specifically for breakfast. “I just got here and decided to go for it.”

Lisa Williams, 36, an executive assistant at a lobbying firm, stood over a trash can to peel the ­marigold-colored slice of American cheese off her Sausage McMuffin — a second choice after she realized that the sausage biscuits weren’t on the all-day menu. It wasn’t the first time McDonald’s has let her down: She recalled walking in once a few minutes after 10:30 a.m. with her 9-year-old son, Liam, too late to get breakfast. Her kid is a big fan of off-hours breakfast.

“I have some friends that call it ‘brinner,’ ” she said. “Moms do that.”

Back at U Street, Marjorie Jones, a crew member sweeping the floors, said that the new breakfast hours didn’t add too much to her workload. In the kitchen, where equipment was emitting a series of mechanical beeps, the cooks maintained one grill at a lower temperature to cook the eggs. Breakfast was selling well, she said, but she thought it would be even better late at night, when young people were on their way home from a long night out.

“They can come in from the bar,” she said. “Like at 2 a.m.”

In breakfast person time, that’s Egg McMuffin o’clock.