JUPITER, Fla. -- The timeline is blurring. Less than 24 hours after general manager Sandy Alderson said Johan Santana was at least 10 days away from throwing off a mound, Santana did precisely that on a brisk Sunday morning in Port St. Lucie.

It was not a full-fledged bullpen session, with catcher Anthony Recker set up in front of home plate. But it still represented a significant alteration of Santana's Spring Training progression.

The two-time Cy Young Award-winner, who aims to be ready in time for Opening Day, declined interview requests immediately after his session. Instead, Santana brusquely asked reporters to spell S-P-R-I-N-G T-R-A-I-N-I-N-G.

"What's Spring Training for?" he said. "What's practice? To get you better. That's what I'm doing right now."

"He's [angry]," manager Terry Collins said. "He has every right to be."

All offseason, Mets officials said Santana would report to camp in the same shape as any other pitcher, healthy and ready to play. It was to be his first completely healthy spring since undergoing surgery to repair a torn left shoulder capsule in September 2010, and on the first official day of Spring Training, Collins affirmed his own confidence by naming Santana the Opening Day starter.

Days later, the situation changed. Santana, who had been throwing regular bullpen sessions, ceased throwing off a mound. When tests revealed no structural damage, the Mets diagnosed Santana with left shoulder weakness, saying he would appear in a Grapefruit League game around March 10.

That timeline seemed impossible as recently as Saturday afternoon, when Alderson said Santana would not even climb atop a mound until the middle of the month. But less than a day later, Santana did precisely what Alderson said he was not close to doing.

"It's Johan Santana," pitching coach Dan Warthen said. "When he's ready, he's ready."

Warthen said Santana "turned the corner" in his long-toss sessions late last week. Once the left-hander reached distances of 180 feet off flat ground, which he did Sunday, throwing off a mound became the next logical step.

For this team, the disparity between plan and execution is nothing new. The Mets also expected closer Frank Francisco to be ready for Opening Day, despite offseason surgery to remove a bone spur from his right elbow and a series of personal problems, which resulted in him arriving at camp with elbow inflammation. But Francisco has yet to throw off a mound, and is now a long-shot for Opening Day.

Mets officials described Santana's situation in detail on Saturday, saying the left-hander reported to camp believing he could ramp up his throwing program as aggressively as he did in his 20s. As a result, Santana chose to rest during the offseason, limiting his workouts to weights and conditioning.

But a week shy of his 34th birthday, Santana discovered he could not build arm strength as quickly as in the past. The left-hander displayed a lack of velocity in his late-February throwing sessions, prompting the Mets to diagnose him with shoulder weakness.

Every bit of progress since that time has been riddled with uncertainty.

The Mets have publicly dampened their expectations that Santana will start on Opening Day, acknowledging that he could actually start later in the first week of April. Even if Santana begins the season on the disabled list, backdating rules would allow him to return in time for the sixth game of the season.

So in essence, missing Opening Day may not be a significant issue for Santana. Of greater concern is the potential for something worse, given his already-delayed timetable.

Perhaps throwing off a mound Sunday, nine days ahead of his new schedule, was Santana's way of alleviating that anxiety. Collins said Santana grew angry at everything written about him in the local newspapers Sunday morning, and Warthen suggested he may have used Alderson's comments as motivation.

"I'm not surprised at anything he does," Collins said. "He's not happy with all the attention that something as minor as that has gotten, and he'll get himself ready."