It is essential that correct temporal order of cellular events is maintained during animal development. During post-embryonic development, the duration of development depends on external conditions, such as food availability, diet and temperature. How timing of cellular events is impacted when the rate of development is changed is not known. We used a novel time-lapse microscopy approach to simultaneously measure the timing of oscillatory gene expression, seam cell divisions and cuticle shedding in individual animals during C. elegans larval development. We then studied how timing of these events was impacted by changes in temperature or diet, and in lin-42/Period mutants that show strongly perturbed and heterogeneous timing of larval development. We uncovered significant variability in timing between individuals under the same conditions. However, we found that changes in timing between individuals were fully explained by temporal scaling, meaning that each event occurred at the same relative time, when rescaled by the total duration of development in each individual. Upon changing conditions, we found that larval development separated into distinct epochs that differed in developmental rate. Changes in timing of individual events were fully captured by temporal scaling for events occurring within each epoch, but not for events from different epochs. Overall, our results reveal a surprisingly simple structure that governs changes in timing of development in response to environmental conditions. The unexpected observation of continued development and accurate temporal scaling in growth-arrested lin-42 mutants rules out a mechanism that explains temporal scaling by linking developmental timing to body size.