NEW YORK - A day after he once again delayed the reopening of most public schools, Mayor de Blasio on Friday couldn’t promise that his newest timeline would hold.

“So again, for those parents who are watching, you’ll guarantee that by October 1, all the public school students who want to be in school will be in school?” asked MSNBC’s “Morning Joe” host Willie Geist.

“I need the healthcare situation to cooperate always, but I want to tell you I think based on everything that I’m seeing,” de Blasio said, citing mask-wearing and social-distancing compliance. “I feel very confident about that date.”

The city on Thursday announced a new phased-in approach to returning students to the classroom, saying teaching shortages were still being addressed and buildings were still being readied.

Early-childhood and special-education students will start in-person learning on Monday as planned but older grades aren’t set to start until either September 29 or October 1.

The change marks the second time the city has pushed the date for opening schools to students.

De Blasio has been widely criticized for not earlier addressing teacher shortages and ventilation challenges.

Teachers and principals begun warning the mayor months ago of steps that must be taken to execute the system’s mix of in-person, blended and remote learning.

The mayor more recently has been asked why a phased-in approach couldn’t be relayed sooner to keep families from scrambling.

“It got harder and harder as we went along to try and make the different adjustments,” he said later Friday on WNYC’s “The Brian Lehrer Show.” “And as I said, the staffing situation got complicated because it was often changing. So there were real challenges here that we foresaw but in practice were more difficult than anyone realized.”