That means now, because it appears that neither of the 37-year-olds will be back next season.
Former Italy and AC Milan defender Nesta has already indicated he will retire at the end of the Major League Soccer season, and Di Vaio said this week that he may also quit for family reasons, even though he would prefer to play another year.
"No one knows what next year's going to bring," Bernier said Friday. "There's personnel that we didn't expect to be here a long time and we have to take advantage of it.
"If they're here next year, great, but this is the season where the team's in good position. It's our second year (together). We know each other better and you have to take advantage of these moments and these players who are maybe in their last year, like Marco."
The Impact (13-7-6) are unbeaten in their last four games and much of the credit goes to DiVaio, who has six of Montreal's 11 goals in that span. The former Bologna striker leads MLS with 17 goals.
They will be looking for another three points when they face the struggling Columbus Crew (9-14-5) on Saturday afternoon.
Lately, the stocky Di Vaio has looked like he could play a few more years, but he said this week he will decide with his family whether to stay on after the 2013 campaign. Either way, he said he will play his best until the end of this season.
"It's great to have him," added Bernier. "I take every game with him like it's the last because you never know.
"It could be he comes back, it could be he doesn't, but this is the year where the group has to see that we can do something that will set the standard for the future. Next year, I hope we have another player like Marco. You never know, but I'm just going to enjoy 2013 as long as it lasts."
The Impact slumbered through the summer and were in a 1-4-3 slump when they found their legs again on Aug. 17 with a 2-1 win over D.C. United. They followed with a 5-0 win over Houston, a 0-0 draw in Philadelphia and last week's 4-2 victory at New England, their first road win since June.
Bernier said the turnaround began with a tweak in their formation to a 4-2-3-1, adding a second holding midfielder to give opponents less room to run in the middle of the field.
"We were leaving our defence exposed against teams that are athletic and can play one-on-one," he said. "We went back to a formation that was very helpful to us at the end of last year.
"Once we had six defending players, it made (opponents) go outside. And we know that with the towers we have in the back (Nesta and Matteo Ferrari), they can cross the ball all day but they're not going to score that many goals."
It started with Bernier and newcomer Hernan Bernardello playing just in front of the defence, but an ankle injury that will shelf the Argentine for four to six weeks gave Collen Warner a chance to get back in the starting 11 last week, although he looked a little rusty.
It also gives Bernier a chance to sneak into the attack from the back if there is an opening.
The 33-year-old had a pair of goals in New England, although both were on penalties. Di Vaio had the other two using the move that has become his trademark, a quick cut inside to lose the defender and right-footed shot inside the far post.
It helps that the whole team looks to have rediscovered its form.
"People forgot in June and July very easily how well we were playing in March, April and May," said Bernier. "When you come down to the wire, you see guys that have character, guys that are used to winning and know how to step up their game when you really need it.
"We know this could be a special year if we all are together, like we were at the beginning of the season and like we are now."
The Impact seem to struggle against Columbus. The Crew got a late goal from Dominic Oduro to grab a 1-1 tie in Montreal on April 14 and beat the Impact 2-0 at home on June 15.
But they have been in a rut in recent weeks. After losing eight of 11 games, coach Robert Warzyche was replaced by former Crew player Brian Bliss on Sept. 2. Bliss is 1-1-0 as interim coach, winning 2-0 over Houston and losing 3-0 in Kansas City.
Impact captain Davy Arnaud once played under Bliss with Kansas City and liked what he saw.
"He's going to demand that they're hard to play against," said Arnaud. "The first game he was in charge of, they looked very good at home. Last week it was tough in K.C. for them, but they have players that can be dangerous.
"They have a new coach, which will give them some extra motivation. And they're in a situation where they need to get points to get back in the playoff hunt. So it's going to be tough."