Havana, Cuba (CNN) -- Diana Nyad is back at it again -- once more in the waters off Havana and heading, she hopes, to Key West, Florida.
The 62-year-old endurance athlete jumped into waters off Cuba on Saturday afternoon, a day earlier than she and her Xtreme Dream team had originally planned, according to her Twitter page. If all goes well, she will swim some 103 miles and 60 hours before arriving in the Florida Keys.
"Right now, (the water) is fantastic and so (the team) has been brainstorming and thinking, we've got to get out there," Nyad said at a Saturday news conference, explaining the decision to start early.
Shortly before 10:30 p.m. Saturday, nearly seven hours into her journey, a new Twitter message from Nyad's team indicated the swimmer had been "stung by a jellyfish." An update a few minutes later indicated she was stung at 8:40 p.m., "was treated and continued swimming."
"(Nyad) is OK and strong," the message said.
Nyad has tried three times before to venture across the Straits of Florida. Each attempt ended prematurely -- starting in 1978 when rocky seas left her battered, delirious and less than halfway toward her goal and twice last year, once done in by an 11-hour asthma attack and later thwarted by box jellyfish stings.
But those aborted swims haven't deterred her, and she insisted earlier this week that "I'm ready."
"I'm feeling some pressure," she said Friday. "I'm feeling tremendous inner pressure that this has got to be it, this has got to be the last time."
She's in the water without a physical shark cage, relying on electronic shark repellent and a team of divers to keep them away. Sharks are just one of the many challenges the American citizen will face, from the sheer physical strain to smacks of jellyfish and the whims of Mother Nature.
That latter consideration drove the decision to push up the scheduled Sunday start time.
The wind is predicted "to be getting really calm by (Sunday) morning and staying calm ... through Monday, and coming up a little bit on Tuesday but still just fine for us to get in," Nyad said.
The hope is to avoid deteriorating conditions caused by stronger winds expected Tuesday night and into Wednesday, which happens to be Nyad's 63rd birthday.
"We've got to get out there," she said.
In the 1970s, Nyad was unstoppable. In addition to winning multiple swimming marathons, she was one of the first women to encircle the island of Manhattan, and she holds the world's record for longest ocean swim -- 102.5 miles from the island of Bimini in the Bahamas to Jupiter, Florida.
She said Saturday that she was 8 years old when she first dreamed about the possibility of swimming across the Straits of Florida. -- At the time, she was in Cuba on a trip from her home in Florida in the 1950s, before Fidel Castro led a Communist takeover in Cuba and its relations with the United States soured.
"I used to stand on the beach and I said to my mother, 'I wonder if anybody could swim over there," Nyad recalled saying, while pointing to the Keys.
While admitting that she's a slower swimmer now than she once was, Nyad insists that in her 60s she still feels "vital (and) powerful" -- and definitely "not old." A successful swim ideally will inspire people her age and older not to let their age hinder them, Nyad said.
"When I walk up on that shore in Florida, I want millions of those AARP sisters and brothers to look at me and say, 'I'm going to go write that novel I thought it was too late to do. I'm going to go work in Africa on that farm that those people need help at. I'm going to adopt a child. It's not too late, I can still live my dreams,'" she said.
CNN's Matt Sloane contributed to this report.