A number of distributed applications require communication services with Quality of Service (QoS) guarantees. The QoS provisioning issue in the Internet has been addressed by the IETF with the definition of the Integrated Services (IntServ) and Differentiated Services (Diffserv) frameworks. Resource reservation mechanisms on which these models are based are totally time-unaware. Yet, we believe that, in some cases, associating a time interval to network resource reservations could be useful for both users and network providers. In this paper we present a distributed scheme for time-dependent reservations in QoS-enabled IP networks. We also show how the standard signalling protocol RSVP may support this new reservation style, with only a few minor modifications. Finally, we present a first prototype implementation of the major component of the proposed architecture and we provide some hints on future applicability scenarios of the advance reservation paradigm and its impact on related topics such as policing and charging techniques in QoSenabled IP networks.