British adventurer Sir Ranulph Fiennes has suffered a potential setback in his bid to complete seven marathons in a week.
Sir Ranulph will raise money for heart research
The explorer was delayed in his departure to King George Island in Antarctica on Sunday by the weather and logistical problems.
He was due to start running his first marathon on the Island at 0600 GMT.
It is possible that the team will also be forced back to the Falkland Islands if their plane cannot land.
A spokesman for the team told BBC News Online: "The clock doen't start ticking until he starts the first marathon.
"From then he has 168 hours to complete the rest. There is some slack in the schedule."
Marathons are also planned for Santiago, Sydney, Singapore, London, Cairo, and New York.
His efforts will raise money for the British Heart Foundation.
The 59-year-old, who lives in Exmoor, had an emergency by-pass operation at Bristol Royal Infirmary in June.
A spokesman for Sir Ranulph said that despite possible concerns over his health, he had only taken out ordinary holiday insurance.
After the cold of Antarctica, there will be two more marathons before hitting the humidity of Singapore.
"That might cause a problem because by then we'll be very debilitated and more easily exhausted than on the first marathon because of lack of time to put all the correct things back into your body," Sir Ranulph said.
"Normally one is advised to rest for three weeks to recuperate between a typical marathon in an English-type climate."
He will then fly to London and run in the morning of 31 October before jetting to Africa to begin his second marathon in a day just before midnight in Cairo.
Sir Ranulph will finish in the official New York marathon on 2 November.
"We've been advised by then that we won't be running in a straight line, so if we get in people's way we hope they'll be patient," he said.