Mayor Bill de Blasio pushed back a meeting with a group of blind residents affected by the Chelsea terror attack on Tuesday — giving himself an extra half-hour to sip coffee with his wife and hit the gym.

Hizzoner, whose poor attendance record includes once being late for an airplane crash memorial in the Rockaways, was scheduled to express the city’s sympathy to residents of the Selis Manor facility for damage caused by the pressure-cooker explosion on West 23rd Street.

The meeting was set for 11 a.m., but city officials announced about an hour-and-a-half earlier that de Blasio would be a half-hour late.

Little did the residents know that the mayor wasn’t busy with important city business while they waited — he was in Brooklyn working on his physique.

“He should have came on time to talk and he could have went to the gym after,” said facility resident Doug Coffman, 66, who added he voted for the mayor, but is now outraged.

The mayor’s relaxing morning began when he and first lady Chirlane McCray left Gracie Mansion, on Manhattan’s Upper East Side, in a caravan of SUVs at 8:23 a.m. and arrived in Park Slope at 8:57 a.m., Post reporters witnessed.

They headed to their favorite coffee shop, the Colson Patisserie, where they were enjoying a nosh at 9:21 a.m. — exactly when City Hall put out an email announcing the mayor’s delay.

A reporter then watched de Blasio and McCray stroll over to the Prospect Park YMCA, where they each spent about 90 minutes inside.

McCray left the Y at 10:55 a.m. while de Blasio emerged around 11:05 a.m., the reporter observed. He arrived in Chelsea shortly before 11:30 a.m.

De Blasio first visited the Orangetheory Fitness center, which had been damaged in the Saturday attack that left 31 injured.

He then spoke for several minutes with Homeland Security Secretary Jeh Johnson before heading into Selis Manor, where he shook hands with people for about 30 minutes before leaving.

Ruben Coellar, a manager at VISIONS — a program at Selis — said the delay and shortening of de Blasio’s visit was dictated by City Hall.

Coellar said he had spoken earlier with mayoral aide Javon Coney, who said that “basically they were running behind and that it was pushed back to 11:30.”

A de Blasio spokesman insisted the mayor’s schedule was changed because he “wanted to connect with Jeh Johnson” — and claimed the gym visit had nothing to do with the delay.

“Had we kept the original slot we wouldn’t have been able to (our event would have been going on during Johnson’s stop at the site),” press secretary Eric Phillips wrote in an email.

Additional reporting by Michael Gartland and Bruce Golding