Technical Abstract: Cotton, Gossypium hirsutum L., plant growth is an important time-specific agronomic character that supports the development of squares, flower production, boll retention, and yield. With the use of a mixed linear model approach, we investigated 14 cotton chromosome substitution lines and their chromosome-specific F2 hybrids for genetic changes in plant growth that was measured during the primary flowering time for two environments. The changes in additive and dominance variances for three time-specific traits, plant height, number of mainstem nodes, and internode length were reported, showing that additive effects for these three traits were a key genetic component after initial flowering occurred in the field. Time-specific genetic variance components were also detected where phenotypic values observed at time t were conditioned on the events occurring at time t-1, demonstrating new genetic variations arising at several time intervals during cotton plant growth. Results also revealed that plant height and number of mainstem nodes, and plant height and internode length shared some common influence due to additive effects during plant development. With the comparative analyses, chromosomes associated with the genetic changes in plant growth were detected. These results should add new understanding of the genetics underlying these three time-specific traits in cotton.