What difference does time and weather make? These are pro yacht racers. They know how fast they are going, the have GPS, and they write their position in a log. Sailboats have a hull speed. It is completely impossible that they covered 15,000 miles in that time, particularly without knowing their boat was going twice as fast as hull speed.
This race occurs over several weeks. Don't know what time you mean. This is what was called "the roaring forties" by 1800s sailors. The racers like it because the weather is always windy. Over the course of a week, indeed a day, the weather could change. The boats were often hundreds of miles apart, so each boat could be in different weather.
What difference does it make?