The Time-AgLOTOS algebraic language and its true concurrency semantics proposed in this paper provide a theoretical foundation to develop on-the-fly planning of actions to be executed under timing constraints. We first show how to produce an intermediate structure called Spatio-Temporal Planning System (STPS). The STPS is a contextual action-based model which provides a formal description of the possible execution plans that globally achieve agent's intentions. The compactness of this structure takes profit from the expression of the action timing constraints and the spatial requirements. We then concretise the possible execution plan by deriving a finite representation of spatio-temporal regions of STPS. As a result, contextual and strategic decisions can be handled in real-time by the agent.