The holy month of Ramadan, one of the most important periods on the Islamic calendar, began on Friday when Muslims around the world fast from dawn until dusk.
That presents an acute problem for athletes and while Habash, like other Egyptian Olympians, has been given license by the High Egyptian Islamic Council not to fast during competition days, he will obey the rules during training at the south coast town of Weymouth, albeit on Egyptian time.
"I can't eat during the day, and I can only eat after sunset, but I choose to fast according to Egyptian time, which makes it easier," Ahmed, who will compete in the men's RS-X fleet, said.
Sunset in Cairo will actually correspond to 1800GMT in Weymouth, meaning Habash will not have to wait quite as long to re-fuel after a hard day on the water.
"During the actual races I am not going to fast, but it does mean when I return home I'll have to re-fast, but only for the five days that I miss," he added.
Algeria's team spokesman Mohammed Azzoug said there were no hard and fast rules for team members.
"It's a very personal thing," he told Reuters. "We just give them the basic information and let them make their decisions."
"I'm not quite sure about the Egyptian guy though," he added. "Imagine if he was in Australia, it would be the complete opposite of what you are supposed to do."
Somalian 1,500m runner Mohamed Mohamed Hassan is not so relaxed.
"It's a blessing month," he said at a welcome ceremony at the Olympic Village in east London, an area with a huge Asian population and near one of the capital's oldest mosques.
"I have been waiting for this month for the past 11 months, it's a month we are very happy to welcome.
"As an athlete it can get difficult but I'm ready to fast and to train and to get through this difficult month."
Team mate Zamzam Mohamed Farah added: "It's a religious matter. I'm just as fast and I don't think it will affect me."
London 2012 organisers say they have catered for the needs of the 3,500 athletes faced with fasting from the early hours of the morning until gone 9pm local time every day.
A 24-hour catering service in the athletes village means they will be able to eat late at night while they offer "fast-breaking" packs which include water, energy bars and fruit.
There are also multi-faith areas where athletes can perform their daily prayers.
It is a sensitive issue, particularly in an area that boasts 250,000 Muslims. Thousands, some in flowing white robes, gathered at the numerous mosques that can be found around the Olympic Park on Friday to mark the start of Ramadan.
Thousands of Muslim Olympians and family members are expected to visit the mosques over the coming weeks for prayers and other Ramadan activities.
"This year we are expecting a higher number of people to come through our doors," Salman Farsi, an East London Mosque spokesman, told Reuters on Friday.
"Today is the first day. The whole place is buzzing."
Opinion is divided among local worshippers, however, about whether athletes should be excused.
"It should be an individual judgement call. I don't think the Olympics is a sufficient enough reason to decide not to fast," said Yahya Alkasmiyah, a charity worker whose family is originally from Bangladesh.
"There are people who are doing all sorts of challenging things outside the Olympics as well. It may actually enhance and boost (athletes) morale and give them an additional boost."
Algeria's Azzoug said there were no signs pointing to Mecca in athletes' bedrooms in the village, but it was not a problem.
"Now they have iPhones you can easily find out which direction it is," he said.