WASHINGTON — President Biden’s highly anticipated “big boy” press conference Thursday — his first formal solo press conference in Washington since 2022, where he will address increasing calls to bow out of the 2024 race — has been delayed by one hour and is now scheduled to begin around 6:30 p.m.

The new time means that clips of the 81-year-old president stumbling again — or exceeding expectations — likely won’t be ready in time for widely watched network evening news programs.

A White House official told The Post that the event was delayed “due to NATO schedule,” which also began later than expected Thursday.

Democrats who support Biden are anxious about the event at Washington’s Convention Center — which will be his first time formally facing a room full of reporters in Washington since November 2022 and his first extended Q&A session with journalists since his confused June 27 debate performance.

“I feel like the narrative needs to change. So either Dems need to get behind Biden or he needs to step aside. But we are losing time,” a Democratic source close to the White House told The Post.

“His press conference is another make-or-break moment.”

The source said there are no indications yet that Biden and his diminished inner circle are seriously considering him stepping aside as more Democrats in Congress ask him to do so in the wake of his disastrous CNN debate performance.

“I have heard folks around him are more dug in,” the source said. “It’s just hard to know because the circle is getting smaller.”

White House press secretary Karine Jean-Pierre has repeatedly referred to the event as a “big boy” press conference where many reporters will be called upon — with the phrase irking some fellow West Wing staffers, who view it as infantilizing the commander-in-chief.

Biden advocates hope he will provide a lucid and forceful defense of his performance and plans for another four-year term — as he did during his annual State of the Union speech to Congress in March — but fear that anything less will further sink his viability.

The president told Democratic governors at the White House last week that after the debate, he had decided to prevent recurrences of his on-stage issues by avoiding public events after 8 p.m.

Still, some Democrats predicted that even a solid performance wouldn’t reverse the damage already done.

“The notion that the President is going to be saved by this [upcoming Lester Holt] interview or that press conference misses the forest for trees,” Rep. Ritchie Torres (D-NY) tweeted Thursday.

“Neither the press conference tonight nor the NBC interview on Monday evening will offer the President the political salvation he seems to be seeking.”