Using the AdS/CFT correspondence, we will discuss physics of thermalization for strongly coupled systems in the presence of a chemical potential. In particular, we will focus on a time-dependent bulk (toy-model) description that interpolates between a pure AdS and an AdS-Reissner-Nordstrom background. In such cases we will argue that non-local operators, such as the entanglement entropy sets the time-scale for thermalization. In the presence of a chemical potential, the thermalization time has an intriguing non-monotonic behaviour as a function of the parameters in the thermalized state. We will also discuss a rather interesting connection between the strong sub-additivity property of entanglement entropy in the boundary theory with the null energy condition in the bulk.