Time synchronization is a critical piece of infrastructure in any wireless sensor network. Time synchronizing nodes are nodes which are responsible for propagating time in the network. Other nodes in the network synchronize themselves with respect to the synchronizing nodes. For various reasons, it is desirable that the number of such nodes is minimized. In this paper, we consider selection of time synchronizing nodes for two protocols viz. a protocol that helps propagate absolute time in the network and another protocol that provides nodes with local relative timescales. We show that the problem of selection of minimum number of time synchronizing nodes for the two protocols is NP-Complete. We then consider selecting time synchronizing nodes for one of the two protocols, Reference Broadcast Synchronization (RBS) protocol, present simulation results. We further present a fault tolerant selection of synchronizing nodes for RBS.