A solid sphere, a hollow sphere, and a disc, all sharing identical...

Since the friction is insufficient to permit pure rolling, all the objects will slip as they move down the incline.

The kinetic friction acting on each object is $f_k = \mu mg \cos \theta$.

The equation of motion for the center of mass is given by $mg \sin \theta - f_k = ma$.

Substituting the value of $f_k$, we get $a = g(\sin \theta - \mu \cos \theta)$.

The linear acceleration $a$ is independent of the shape, mass, radius, and moment of inertia of the objects.

Since all objects are released from rest and travel the same distance along the incline with the same acceleration, they will all require the same time to reach the bottom.