The purpose of this study was to explore college students' recognition of temporal magnitudes associated with durations of scientific changes through construct validation of a 30‐item instrument. We administered the instrument to 514 students from 10 higher education institutions in the United States. Among them, 419 students took the instrument at the end of science courses. The remaining 95 students took the instrument before and after a course on cosmic evolution, and additionally answered whether they knew, estimated, or randomly guessed at the temporal magnitude of each item in the instrument. We also collected exam scores for the cosmic evolution course students. Using descriptive statistics and a Rasch analysis, we investigated construct validity of the instrument in terms of psychological relevance, psychometric conformity, and instructional sensitivity. Results of this study indicate that (1) the temporal‐magnitude recognition ability is a measurable construct, (2) extremely small duration items are significantly more difficult for students to recognize accurate temporal magnitudes than other duration range items, (3) direct knowledge of the magnitude contributes to the measurement of the construct, (4) the instrument is sensitive to instruction designed to improve the construct, and (5) the temporal‐magnitude recognition ability is not significantly correlated with knowledge about the related scientific changes. © 2010 Wiley Periodicals, Inc., Inc. J Res Sci Teach 48: 317–335, 2011