Nothing to do with barrel length. 1in12 means the bullet rotates once in every 12". This equates to, when the bullet leaves the muzzel and travels 12" it has rotated once.
A 1in 8 has rotated once in 8" therefore it has more spin, it has more giroscopic effect and more stability
I understand that the twist is the rate of rotation of the rifling. 1:10 is same rate regardless of length, therefore the torque is constant being a product of the rate.
Referring to length I meant the bullet is under the influence of the torque for longer. I've always understood that to mean more spin in RPM.
Eg, Take a 22 rifle and a 22 pistol (in the same twist rate). During flight the rifle round will spin faster in terms of RPM. Although come to think of it, that would be mainly a product of increase muzzle velocity I suppose.