In valid-time indeterminacy, it is known that an event stored in a temporal database did in fact occur, but it is not known exactly when the event occurred. We present an extension of the tuple-timestamped temporal data model, called the possible chronons data model, to support valid-time indeterminacy. In the possible chronons data model, each event is represented with a set of possible chronons, delimiting when the event might have occurred, and a probability distribution over that set. We extend the TQuel query language with constructs that specify the user's credibility in the underlying valid-time data and the user's plausibility in the relationships among that data. We outline a formal tuple calculus semantics, and show that this semantics reduces to the determinate semantics on determinate data.