In rats, 'time cells' in the hippocampal CA1 fire sequentially at particular moments in between salient events and thus have been proposed to encode elapsed time. However, previous studies of time cells involved moving animals, and the activity of these cells might therefore be related to movement rather than time. Here, the authors recorded from time cells in immobile, head-fixed rats performing an olfactory delayed matching-to-sample task. Many CA1 neurons activated at particular moments during the delay period in this memory task and different odour memories were associated with distinct patterns of time cell activity. This suggests that time cells may encode the 'flow of time' associated with a memory.