Convexity splitting like schemes with improved accuracy are proposed for a phase field model for surface diffusion. The schemes are developed to enable large scale simulations in three spatial dimensions describing experimentally observed solid state dewetting phenomena. We carefully elaborate the loss in accuracy associated with large time steps in such schemes and show the existence of a maximal numerical timestep to achieve a prescribed accuracy. We demonstrate the increase of this maximal numerical time step by at least one order of magnitude using a Rosenbrock method. This convexity splitting scheme with improved accuracy is used to study the effect of contact angle on solid state dewetting phenomena.