Hall effect sensor operational distance from magnet
That depends a bit on how the magnet is oriented with respect to the sensor.

I would approach this question by first making the approximation that your magnet is a point dipole. Even though it is a cube, this approximation will be reasonable when you are an inch or so from the cube.

Therefore, you can use this equation for flux density at a given point. You will need to figure out the magnetic moment based on the specifications from the magnet manufacturer.

Then, determine the critical distance which results in a field of 35 Gauss.