When is it too early to call a National Hockey League rookie a star?

In Connor McDavid’s case, it was only a matter of seconds.

Everyone knew that the Oilers’ center and captain had the goods shortly after he was out of diapers.

In the case of the Islanders’ new ace, Mathew Barzal, a bit more time will be required — maybe a month or two, maybe even less.

Although the Islanders were beaten, 2-1, by McDavid’s Oilers in overtime Tuesday night, it was Barzal who outplayed Edmonton’s captain, who had won the Hart and Art Ross trophies last season.

“Barzal was the best player on the ice,” wrote the Edmonton Journal‘s Hall of Fame columnist Jim Matheson.

The Isles’ dazzling freshman was the architect of Jordan Eberle‘s goal in the second period. It was merely one of a cavalcade of Barzal’s highlight-reel moves.

“Mathew set up a dozen other terrific scoring chances on another wondrous evening for the 20-year-old,” added Newsday‘s Arthur Staple.

A similar collection of kudos were delivered on Nov. 5 when Barzal set a club rookie record with five assists in a 6-4 win over the Colorado Avalanche.

MSG Networks analyst Butch Goring, who has been studying hockey ever since his rookie year in 1969-70, waxes eloquent over Barzal’s assets and The Kid’s future.

“Mathew’s skating is his forte,” said Goring. “The guy can fly — just like McDavid. Barzal’s speed allows him to do a lot of things that others can’t do.”

A year ago, the best description of Barzal after a two-game audition with the Islanders was bust.

General Manager Garth Snow figured his draft pick needed more refinement with the Western Hockey League Seattle Thunderbirds.

The demotion so thoroughly agreed with Barzal that the Coquitlam, British Columbia native spearheaded his club to the WHL Championship. In addition, Matty was named the playoffs MVP.

[Watch Friday’s Islanders-Stars Game on MSG+ and Download Free on MSG GO]

In his second time around, Barzal showed up at training camp as if he was fueled with a confidence serum.

“I decided to take it practice by practice,” Mathew recalled, “and hope to be noticeable whether in a scrimmage or an exhibition game. Then it would be up to management to decide my future.”

The decision was positive with center Barzal and right-wing Joshua Ho-Sang, both impressive in the early going. But, eventually, the latter was demoted to Bridgeport while Mathew’s magnificence became more apparent by the game.

MSG Networks Islanders play-by-play broadcaster Brendan Burke detected a difference between the 2016 Barzal and the current model.

“He’s a whole different player,” asserted Burke. “The year in Juniors made him better. He doesn’t even look like the same guy as last year. It’s crazy to think that. But this time around he has set himself apart.”

Heading into Friday night’s game against the Stars in Dallas, Barzal has played in every one of the 15 contests for the Brooklynites. He has totaled 14 points and is breezing along with a six-game point streak.

What seasoned observers such as Matheson have noticed, is that Barzal seems to lift his play as the game’s importance increases.

Prior to McDavid’s overtime score, Barzal just barely missed setting up John Tavares for the game-winner.

“I love big games,” said Barzal, “and pressure moments and being right in the midst of a tight game. I pride myself on being a big-time player.”

Since being moved on to a line with Eberle and Andrew Ladd, Barzal has helped his mates lift their game.

When I asked Eberle what makes his young center so special, he singled out Matty’s speed and savvy. I put the same question to coach Doug Weight.

“Mat’s confidence with the puck,” said Weight, “and his ability to change direction and create opportunities for guys around him are among his assets.

“He also has the uncanny ability to find people while he’s shifting his weight and turning away from checks. Instantly he sees the ice. When the hands match the brains those plays can be made.”

Barzal will admit that he’s still refining his game and with three-quarters of the season ahead, he should be a significantly more improved player by April.

Goring figures that the Barzal-Eberle-Ladd unit could be as decisive as Captain John Tavares’ first line in pushing the Isles into the post-season.

“Mat is coming into a really nice situation for the Islanders,” Goring said. “They can’t rely on Tavares to always score goals. Barzal comes along playing with Ladd and Eberle, and they’ve really hit it off.

“When you start getting two lines that are skating consistently and the power play starts to be good, and you take care of the puck, you start to become a good team.”

MSG Networks Islanders host Shannon Hogan, who has kept an Argus eye on Barzal’s improvement graph, also perceives a major boost in his confidence.

“During his last year in Juniors,” Hogan pointed out, “Mathew worked on improving in specific areas. His skill always was there but there was fine-tuning to be done.

“That extra year was really valuable for him. Then, this September he had a good camp and then a good couple of weeks into the season. It’s not that he’s got a cocky confidence now; it’s just plain confidence.”

Just how much better can Barzal become as an Islander?

“He’s a stud,” Weight concluded, “and will be a really good player. He believes that he can be great and he wants to strive for it.”

How high Barzal’s star?

How high the moon!

[Watch Friday’s Isles-Stars Game on MSG+ and Download Free on MSG GO]