ADP keeps running ads about solar flairs that force earth into a 25 hour day. Could a solar flair even do that, and what distasters would happen if Earth's orbit changed?

The Earth's orbit dictates the length of a year, not the length of a day. I suppose theoretically a strong enough solar wind could push the Earth further from the sun, lengthening the year. Such a strong solar flare would also probably penetrate our magnetic field and blow away all the atmosphere, water, and life on the planet. We would experience an extremely loud noise, then extreme flames everywhere, and if you managed to survive that, a wind stronger than a billion nuclear explosions would atomize you before blowing your atoms into space.

The length of a day is related to the speed with which the earth rotates. I suppose a solar flare could create a magnetic field that affects the spin of the earth, but any sudden change would again require forces strong enough to basically destroy all life one way or another. Maybe the Earth cracks into several chunks, which would feel like the worst earthquake ever, massive tsunamis, volcanoes everywhere, and then if you survive that, you'd probably freeze to death in a matter of hours as the exposed core cools in the vacuum of space. Or maybe you'd suffocate first due to a lack of atmosphere.

The speed of our spin is being slightly slowed by the moon. We gain about 1.8 miliseconds per century, so it will be a while before we get to 25 hour days. But it is theorized that the emergence of blue-green algae 4.8 billion years ago was due in part to the slowing of the Earth's rotation that allowed it to produce more oxygen every day, leading to an explosion of oxygen responsible for life as we know it.