When the plate tectonics on Earth
The first blocks of continental crust, cratonic arose on Earth in the Archaean, but then began their horizontal movement, but a full range of features of the mechanism of plate tectonics modern type is found only in the Late Proterozoic. Prior to that mantle, perhaps, had a different structure of mass transfer, which played a large role not steady convective flows and turbulent convection and plumes.
In the past, the flow of heat from the bowels of the planet was bigger, so the crust was thinner, the pressure under the much thinner cortex was also much lower. And at much lower pressures and slightly higher temperature, the viscosity of mantle convection currents directly under the bark was much lower than the present. Therefore, in the crust, floating on the surface of the mantle flow, less viscous than today, there were only relatively small elastic deformation. And the mechanical stresses generated in the cortex less viscous than today, convection currents were not sufficient to exceed the tensile strength of crustal rocks. Therefore, there was no such tectonic activity, as at present.