Will rookie Sam Darnold be the Jets’ season-opening starter at QB? (Ronald Martinez/Getty Images)

When the quarterbacks came off the board so early and so often on NFL draft night in April, hope abounded and the countdown began: How long would it take for Baker Mayfield, Sam Darnold, Josh Allen and Josh Rosen to begin changing the on-field fortunes of their franchises?

Perhaps just a bit longer than some might have expected, it turns out.

While this highly celebrated class of rookie quarterbacks remains long on promise, it might end up being relatively short on immediate impact. The second week of preseason games leaguewide arrives now with Darnold, the draft’s No. 3 overall selection, well positioned to vie with Josh McCown and Teddy Bridgewater for the New York Jets’ starting job.

But if Darnold indeed emerges as the Jets’ season-opening starter, he could be standing alone among this rookie quarterback class. For now, at least, it appears that Mayfield will have to wait his turn behind Tyrod Taylor in Cleveland, that Allen probably won’t overtake Nathan Peterman and AJ McCarron right away in Buffalo and that Rosen will begin his rookie season as an understudy to Sam Bradford in Arizona.

So it could be Darnold who gets the first chance to try to prove to his team that it made a wise investment and to convince a fan base that better times truly are at hand.

“It’s been a while since I got drafted, or at least to me it seems like it,” Darnold said this week. “So I’ve been hearing all the buzz and everything for a while now. It’s really cool. It’s really fun to be a part of this organization, and the fans are incredible as well.”

The chance will come soon enough for each of these quarterbacks. All four were drafted in the top 10 — Mayfield went first to the Browns, Allen was taken seventh by the Bills and Rosen was selected 10th by the Cardinals — and each is regarded as a potential franchise quarterback.

But there’s no one-size-fits-all way to go about it. Take the 2004 quarterback class that included the New York Giants’ Eli Manning, San Diego’s Philip Rivers and Pittsburgh’s Ben Roethlisberger. Only Roethlisberger became a starter early in his rookie season. It took the Giants nine games to promote Manning over veteran Kurt Warner. The Chargers kept Rivers on the bench for two full seasons before allowing Drew Brees to leave the team in free agency and clear the starting spot for Rivers.

For some young quarterbacks, such as former top overall picks Tim Couch of the Browns and David Carr of the Houston Texans, early-career struggles can prove ruinous. For others, such as Peyton Manning and John Elway, the initial rookie missteps serve merely as steppingstones to all-time greatness. So who’s to know?

“You have to trust your instincts and play the guy when you think he’s ready,” an executive with one NFL team said this week. “With this group, I wouldn’t play Allen right away. He needs some time. I think the other three guys are ready to play any time. I’m not saying they’re ready to be Pro Bowl guys. But I think you could put them in there and do some things with them and get by. They’d make mistakes. But it wouldn’t ruin them, and they’d do enough good things that you wouldn’t embarrass yourself.”

The Browns, a combined 1-31 over the past two seasons, traded for Taylor as part of the offseason roster upgrade by their new general manager, John Dorsey. Taylor, formerly the starter for the Bills, is a capable placeholder for Mayfield, with a proven ability to avoid turnovers. The Cardinals, in Bradford, have an often-injured but proficient-when-healthy starter, with a career passer rating of 85.1.

The temporary alternatives are less appealing for the Bills and Jets. The Bills reached the playoffs last season with Taylor but decided to begin anew at quarterback and sent him to Cleveland. If Allen is deemed not ready to be the season-opening starter, Coach Sean McDermott must choose between Peterman, a second-year pro who had a five-interception first half in the first of his two starts last season, and McCarron, the former backup in Cincinnati to Andy Dalton. Allen is considered less polished as a passer and less NFL-ready than Mayfield, Darnold or Rosen. But his size, athleticism and dazzling arm strength have prompted comparisons with Carson Wentz, Philadelphia’s prodigious quarterback who might have been the league MVP last season if not for a December knee injury.

The Jets re-signed McCown, a respected pro but a backup for most of his NFL career, and added Bridgewater, the former starter in Minnesota returning from a devastating leg injury suffered two years ago, along with drafting Darnold. But the future could be now with Darnold, and Coach Todd Bowles wants to see plenty of the rookie during the preseason.

“I can get a fair evaluation of Josh,” Bowles said after one of the Jets’ joint practices this week with the Washington Redskins in Richmond. “I’ve seen him quite a bit. I’ve seen Teddy quite a bit. Sam’s the one that has to catch up.”

The Jets face the Redskins on Thursday night at FedEx Field in their second preseason game. Darnold, after missing the first few days of training camp because of a dispute over the final details of his rookie contract, is coming off a crisp 13-for-18 passing performance against the Atlanta Falcons in the exhibition opener, playing with backups. He could get work with the starters Thursday.

“Every time I get in there, I look to get better,” Darnold said. “That’s just who I am as a player. I just try to get in there and get better every single day no matter who I’m playing with because the reps are always the most important. The plays are the same. It’s just the ones, the twos or the threes …. It doesn’t matter who you’re with …. But every single time I get in there, I just look to compete and play my best.”

Another solid preseason outing or two by Darnold could make Bowles’s decision relatively easy.

“We’re happy with what we saw,” Bowles said. “We’ve got some things to build on, as has Teddy, as has Josh. And we’ll go from there.”

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