Title: Extending Search for Hybrid Systems: Action Timing Abstract: Artificial Intelligence tree search algorithms are designed for discrete systems. In order to extend tree search algorithms for hybrid systems, there are two new decisions the search algorithm must make: choice of actions from a continuum, and choice of action timing. In this paper, we focus on principled ways to choose when to branch the search tree. We introduce anytime, depth-first, iterative-refinement algorithms for satisficing and real-time decision-theoretic goals. Further, we discuss iterative adjustment techniques. Finally, we briefly discuss the use of information-based optimization for action timing choices.