A series of end-linked poly(dimethylsiloxane) (PDMS) networks were prepared with different cross-link functionalities and molecular weights. This was achieved by simultaneous end-linking and self-condensation of a trifunctional silane cross-link precursor. These networks had a nonpolar naphthalene chromophore covalently attached to a fraction of the cross-link junctions. We probe the time-dependent reorientation of the naphthalene, and infer reorientation of the cross-links, by determining the time-dependence of the fluorescence depolarization in the picosecond time domain. A two-step relaxation model describes the orientational dynamics. Fast, partial depolarization in a restricted geometry is superimposed on a slower relaxation that completely depolarizes the fluorescence. We determine the two rotational diffusion constants at temperatures varying from 235 to 298 K, while we vary network parameters such as cross-link density, molecular weight, and macroscopic strain. These diffusion constants have an Arrhenius activation energy of 11.4 +/- 0.8 kJ/mol. The fast relaxation is driven by motions of a few chain segments; this process is dominated by the density of the network polymer around the labeled cross-links. The slower, complete reorientation is driven by cooperative motions of a larger number of chain segments connected to the cross-link that are insensitive to steric constraints in the immediate vicinity of the cross-links.