A method including running a local low frequency clock in a node in a network during a battery conserving sleep mode, waking from the sleep mode at a time boundary determined by the low frequency clock, updating a representation of a master time based on a calculation and the time boundary, advancing the representation of master time based on a local high frequency clock while the node is awake, receiving a time synchronization signal from a node in the network, updating the calculation based on a difference between the representation of master time and a time provided in the time synchronization signal, setting a new time boundary, and returning to the sleep mode.