Six experiments examined human performance on a modified temporal generalization task when either 1 or 2 standard durations were encoded. In most conditions, participants were presented with a 1st standard duration (A), then judged whether a number of comparison stimuli had the same duration as A. They were then presented with a 2nd standard (B) and again judged whether other comparison stimuli had the same duration as B. Then, after a delay period of 0-45 s, further comparison stimuli were presented, and participants judged whether those stimuli had the same duration as A, without A being represented. A was either the same length as B or shorter or longer than it, so potential retroactive interference effects of B on A could be examined. After a short delay before retesting of A comparisons, the peak of the temporal generalization gradient shifted toward the shortest of the comparisons when A < B and the longest when A > B. The results suggest that certain combinations of delay and interference might render the memory of A unusable, so that a new standard is constructed on the basis of the remembered relationship between A and B, a kind of “false memory” for duration.