For a given stellar mass and orbital radius (assuming a circular orbit), there's not really any wiggle room on how long the planet's orbital period is. Speeding

For a given stellar mass and orbital radius (assuming a circular orbit), there's not really any wiggle room on how long the planet's orbital period is. Speeding up or slowing down the planet requires it to orbit at a different distance. If you meant the speed of a planet's rotation about its own axis, I guess the limit would basically be the point at which it tears itself apart by spinning so fast that its gravity no longer holds it together.