The spacewalk will be broadcast on NASA Television and streamed live online.
According to NASA, during their planned 6.5-hour spacewalk, the astronauts will also install a protective shield on the Pressurized Mating Adapter-3, which was moved from the Tranquility to the Harmony module in March.
"Lot of curveballs this morning", NASA astronaut Kjell Lindgren radioed to the crew from Mission Control in Houston.
Since that time, space fliers from around the world have ventured out on spacewalk after spacewalk to build it into the complex network of living space and experiments it is today, hosting research and experimentation 250 miles (400 km) above the Earth.More news: Oil up on drop in US petroleum stocks, possible OPEC cut extension
The airlock is equipped with two such umbilicals to provide cooling water, power and data while the astronauts are inside the station, preserving the suits' batteries for the actual EVA.
Expedition 51 commander Whiton and Flight Engineer Fischer will replace a large avionics box on the outside of the ISS on Friday, April 12.
Other jobs in Friday's spacewalk plan before the umbilical leak included the setup of a new high-definition video camera and a pair of wireless antennas outside the research complex, plus inspections and repairs of insulation on the station's Japanese robotic arm.
Astronauts kicked off space station construction in orbit in 1998. This is also the 9th time Whitson has taken part in a spacewalk, extending her record as the American woman with the most spacewalks in history.More news: Andy Murray exits tournament, stunned by Borna Coric — ATP MADRID
With a full-duration 6.5-hour spacewalk, Whitson would have moved up to third in the world with almost 60 hours of EVA time over nine excursions, trailing only cosmonaut Anatoli Solovyev, with 78 hours and 21 minutes of spacewalk time over 16 EVAs, and retired astronaut Michael Lopez-Alegria, with 67 hours and 40 minutes over 10 excursions. Initially, White propelled himself to the end of the 8-meter tether and back to the spacecraft three times using the hand-held gun.
An issue with some gear inside the airlock ahead of the spacewalk forced mission managers to delay the start time and shorten the walk in space.
"Oh my gosh, this is attractive", Fischer said as he worked 250 miles above the planet.More news: Shorten's budget is 'bulldust': Treasurer