Studying human development involves describing, explaining, and optimizing intraindividual change and interindividual differences in such change and, as such, requires longitudinal research. The selection of the appropriate type of longitudinal design requires selecting the option that best addresses the theoretical questions asked about developmental process and the use of appropriate statistical procedures to best exploit data derived from theory-predicated longitudinal research. This paper focuses on several interrelated problematics involving the treatment of time and the timing of observations that developmental scientists face in creating theory-design fit and in charting in change-sensitive ways developmental processes across life. We discuss ways in which these problematics may be addressed to advance theory-predicated understanding of the role of time in processes of individual development.