By the time the season opens on October 8, their opening night roster will have been submitted.
With a week left in the preseason, they're getting closer to that point, but questions still remain.
There are still 18 forwards, nine defensemen and four goalies at training camp, and that number will need to be cut down to a 23-man roster.
"It keeps your mind going because you have to come to the rink and it's not just one of those practice days - it's a 'you're battling for a job' day," said Johnny Boychuk. "Nobody's in the clear."
Tuesday night provides yet another opportunity for players in the mix to prove that they belong, and deserve a spot with Boston.
Veterans like Boychuk and Chris Kelly have embraced that fight for jobs as pushing them to be better as well.
"Every year, you're battling for a job. Some people might think that they have the job and that's their right, but you have to come to camp and you have to prove yourself every year and be ready to battle," said Boychuk. "Because if you do that, you're going to be ready for the start of the season."
"Everyone’s pushing each other and everyone’s working hard," said Kelly. "Competition is a great thing for everyone — it makes everyone work that much harder, to know that there are people pushing for jobs, and you either need to push back or you lose a spot. So I think it just helps you in the long run, especially going into the season."
With the roster beginning to take shape, Tuesday night's game won't just be about evaluation and competition; it will also give the Bruins a chance to work on chemistry and timing. It's that combination the Head Coach Claude Julien, General Manager Peter Chiarelli and the rest of the staff will be watching for all night.
The players will be watching for it, too.
"I mean, you just look at the practice roster, the game roster, either roster you see the guys that have worked hard and they've earned a spot to be here right now," said Boychuk.
"Still have some decisions to be made but so far, everybody's battling and competing hard, so there's still some unknowns out there and it will be interesting to see."
Boston's roster against the Islanders will allow all of that to play out.
There's been an ongoing battle for spots on the fourth line. With Gregory Campbell sidelined by a mid-core issue and questionable for the season opener, that has opened up a fourth line spot in the short term. On Tuesday, the trio of Jordan Caron, Craig Cunningham and Bobby Robins will assume that bottom line role.
While Justin Florek, Alexander Khokhlachev and Ryan Spooner won't be suiting up, they're still among the mix of players battling for the bottom six as well.
The versatile Daniel Paille, the only veteran not in the lineup for Tuesday, will take on whichever role is given to him.
Matt Fraser will be in the right wing spot on the third line alongside Carl Soderberg at center and Chris Kelly on the left wing.
Is Kelly any closer to figuring out how the lineup will shake out and where he'll be?
"I was hoping you guys were going to tell me that right now," he quipped to reporters. "No? No, I have no idea. That’s the fun part of camp. It’s just worrying about, to be honest, yourself, and you go out there and work hard and whoever you’re playing with, try to form some quick chemistry and go out there and work hard together."
As Kelly works to find his timing following his offseason back surgery and long layoff from game action, Fraser has done everything in his power to try and earn a spot on this team.
"I think it's pretty obvious that he is making a statement and if he plays the way he has been on a consistent basis, I don't think anybody's going to keep him out of this league," Julien has said of Fraser.
"So it's up to him to maintain that standard, and if he does, he's got a real good chance of sticking."
Along with the young players battling for spots, veteran Simon Gagne still remains on a tryout with the Bruins.
Because Reilly Smith needs to play catch-up and get into game shape before suiting up, he won't be in the lineup Tuesday (neither will Torey Krug, for the same reasons).
While Smith will eventually slot back in with Brad Marchand and Patrice Bergeron, the situation opens up an opportunity for Gagne to play with that duo again, as he did in Saturday's preseason game in Detroit. It's a desirable situation for him, and he'll need to take advantage of it.
As for the "audition" of Loui Eriksson on David Krejci's right wing, Tuesday night is the first time this preseason that Eriksson, Krejci and Milan Lucic will all be playing together in game action.
Lucic has been working to get his hands back following offseason wrist surgery, so that may hinder the meshing process, but the trio will look to start getting in sync.
At the end of the day, three bottom six spots and Krejci's right wing spot are all considered in contention right now.
"We change our minds every day, to be honest with you," Julien has said, of line tweaks and front-runners for spots. "We'll sit one day, we'll have something the next day and 'oh, last night I was doing some thinking here' and it could come from Peter, could come from myself, could come from others, so we change our minds every day."
"Every day is a new challenge and every day we're changing our minds."
Goaltender competition hasn't been mentioned much, but newcomer Jeremy Smith will follow up his first solid performance at TD Garden (and highlight reel glove save) with the starting gig against the Islanders. Niklas Svedberg, still primed for Tuukka Rask's backup role, will be the other goalie suiting up.
And while spots aren't "open" on the back end, there are nine defensemen pushing to get in.
Tuesday will feature the most veteran blueline of the preseason, with Boychuk, Zdeno Chara, Dennis Seidenberg, Adam McQuaid, Matt Bartkowski and Dougie Hamilton.
Since Krug isn't up to speed yet, he'll be sitting out with David Warsofsky and Kevan Miller.
"Just from camp, it's crazy how much depth we have and there's a lot of guys that can play in the NHL," said Hamilton. "So we've got a lot of guys that could play and that aren't playing so I think that just pushes you to keep working hard."
"You're obviously going to play your best, but you know that there's somebody there that can play, too, so you always have to be aware of that."
After Tuesday, there are only two preseason games left, in Bridgeport against the Islanders on Friday and then the final tune-up on Saturday against the Red Wings at TD Garden.
The decisions won't be easy, but they're not supposed to be.
"It means you’ve got a great situation here. It means you’ve got depth and that’s what you’re looking for in an organization," said Julien. "Those problems are tough problems, but they’re good problems."
"At the end of the day, you have to cherish those situations because it could easily be the other way around."