Bill de Blasio, the man who introduced the seven-hour work month to New York’s how-to-be-a-mayor manual, went on “Morning Joe” Friday to deep-six his humiliating LSD trip of a presidential campaign.

“It’s clearly not my time,” said the mayor.

Giggle.

Now here’s the question: When a candidate craters in public and nobody cares, does he make a difference?

Well, maybe these: De Blasio’s departure probably raises the IQ of the Democratic field by a few points, plus the New York hotel industry — which pretty much financed his campaign — can lay down its checkbook for a while.

And now Kaiser Wilhelm has New York to kick around some more — or, as he puts it, “I’m going to continue my work as mayor.”

Oh, goody.

Surely the Park Slope Y appreciates the heads-up, because nothing spiffs up a gym like police security details hanging around all morning.

And if there are not enough vagrants splayed out on subway car benches, a rested and re-energized Bill de Blasio quickly can chum up some more.

Plus the city hasn’t been punked by Andrew Cuomo in months; the governor will be delighted to see his old sparring partner climb back into the ring.

So happy days are here again, and the skies above are clear again — except for those subway bums. Plus collapsing public housing, people shooting at cops, a barely functional public school system, a wife grinding up tax dollars to fuel a make-work mental health project, and so on and so forth.

Geez, no wonder the man ran for president.

The end of his excellent misadventure reduces the number of New York Democrats in the presidential race from three to zero: Sen. Kirsten Gillibrand aborted her own bizarre campaign last month; Mike Bloomberg, who showed a little leg earlier in the cycle, decided to forgo the humiliation.

Predictably, the de Blasio campaign couldn’t break into single digits in the polls — zero is only technically a number, after all — and the wonder of it is that he even tried.

But maybe that’s not so curious, on reflection.

Running for president gave him more freedom to ignore his oath of office, which has always been an administration priority.

The effort presented new opportunities for those with business before City Hall to show their affection for the mayor in concrete terms. This also has been important to the administration — and no doubt Blaz is studying ways to refresh the relationship.

The campaign meant that he had a taller rostrum from which to denounce Donald Trump — the first New Yorker to live in the White House since Franklin D. Roosevelt. This gnaws unmercifully on Empire State Democrats — and while there’s no evidence that de Blasio actually believes what he says, about Trump or anything else, chewing on the president’s leg diverts attention from the administration’s numerous failures.

So there was some utility there after all.

Now de Blasio has only dreams of what might have been — and memories of those 10-person campaign crowds; his mortifying invisibility in the polls; his irrelevance in the cattle-call debates; his virtual inability to raise a legitimate dime, and the rip-saw ridicule he suffered in the media.

Normal New Yorkers are left with this question: How can the fellow even look into the mirror in the morning?

Bob McManus is a contributing editor of City Journal.