The Guinness World Records has no official category for the longest handstand. It does, however, offer a challenge to people who attempt to increase their time in the handstand position.
Guinness instructs people to attempt the longest handstand possible by having their feet straight up in the air, doing it completely alone and without a wall. It also suggests to begin timing as soon as the person's hands touch the floor.
There are handstand records while riding on various objects, such as a skateboard. That record was set by Sam Tartamella when he skateboarded 2,255 feet while in a handstand.