In his view space 'contains an inertial reference frame and provides an electromagnetic reference frame. Time, as a property of space, could be quantified universally as the relative periodic motion of these two frames. This is the simple, logical proposition on which a new theory of physics can be built. It is hardly hypothesis. Time has to be defined in terms of motion.
Motion is relative.
Only two features of space are available, the inertial and the electromagnetic reference frames'. This something he calls a G frame, and he assumes that 'the E and G frames have, when undisturbed, the same mass density and rotate in the same sized orbits of radius r'. One might wish the author had been more explicit about the orbits of the frames. Electromagnetic-wave propagation is explained by the light charged particles of the E frame, gravitation by the heavy charged particles of the G frame. But we must not quibble at a part or two in 100,000.