Playtime is over at Islanders training camp, but the hockey edition of musical chairs has only just begun.

After using the first portion of camp to get the prospects valuable time and experience alongside veterans, Monday’s 6-5 preseason loss to the Devils marked the second straight game in which the Isles rolled out a majority-veteran lineup, though it was not quite as packed with NHL players as Saturday against the Rangers.

There are still two exhibition matches and two weeks worth of practices to determine the outcome of the jigsaw, so Hudson Fasching and Simon Holmstrom — the odd men out of Monday’s game group — need not worry.

The math, though, is going to end badly for at least one of Fasching, Holmstrom, Julien Gauthier or Oliver Wahlstrom.

Four into three does not go, and those four are competing for three spots in the opening-night lineup, which will be reduced to two if Kyle Palmieri is back.

That is a good problem for the Islanders to have, as all four have put in solid training camps so far — to say nothing of prospects William Dufour, Matt Maggio, Arnaud Durandeau and Kyle MacLean, who are unlikely to make the roster, but could make appearances in Isles uniforms at some point this season.

“They’ve very close,” coach Lane Lambert said ahead of the game at Prudential Center. “That’s what we wanted right from Day 1. It’s with those four guys, it’s with other guys in terms of what kind of role or what significance their role is gonna be, whether it be a younger player or a veteran player. But those guys in my mind, they’re making the decision difficult and doing a good job with that.”

Based on what we have seen so far in camp and exhibitions, we know that the top two lines will likely include pairs of Bo Horvat and Mathew Barzal and Pierre Engvall and Brock Nelson.

Anders Lee had been with Jean-Gabriel Pageau for most of camp, but played with Horvat and Barzal on Monday.

The fourth line of Matt Martin, Casey Cizikas and Cal Clutterbuck was all but written in ink before a skate blade touched ice.

That likely leaves spots to Nelson and Pageau’s right up for grabs, though Palmieri should slot next to Nelson if he makes it back.

Depending where Lee ends up, there will also be a spot to the left of either Horvat or Pageau for someone to take.

The captain’s performance on Monday night, though, was a point in favor of him staying on the top line.

“Anders, I could argue he was our best player tonight,” Lambert said. “Competed, battled, drew penalties, got involved. So I thought their chemistry was pretty good.”

Though Fasching, Gauthier and Wahlstrom are all right-handed shots and Holmstrom a lefty, that is unlikely to impact things, Lambert said.

After Holmstrom owned the spot to Horvat’s left for about a week, the potential of Lee moving there throws the whole thing open.

As for the other three, the competition right now is too close to call.

Gauthier skated on the fourth line against the Devils after Lambert tried him next to Pageau on Saturday against the Rangers. Wahlstrom started with Karson Kuhlman and Ruslan Iskhakov — neither of whom are likely to make the roster — in Newark, but rotated to the second line throughout. Fasching was with Nelson and Engvall against the Rangers, then sat Monday.

In other words, it’s anyone’s guess.

The good news for the Islanders is none of the four are making it an easy call for the head coach.

There are good arguments for playing all of them, and the likelihood is that whoever is left out Oct. 14 will not be left out for long.

But that date is when the training camp music will stop.

“It was awesome,” Gauthier told The Post of skating with Lee and Pageau following the 5-3 win over the Rangers. “They’re fun to play with, they work hard. I think we had some great chemistry, some good play. So it’s easy to play with guys like that.”

As for Fasching, Lambert said after the Rangers game that he “looked good” alongside Engvall and Nelson. “He opens up space and room at times for Brock, and I thought Pierre skated good tonight, too,” Lambert said. “I thought there was some chemistry there.”

Aside from a listless first 10 minutes in the opener at Madison Square Garden, the Islanders have played well so far in the preseason, with all four lines getting on the board in the rematch against the Blueshirts.

That does not make Lambert’s job any easier.