FARMERS are often unable to determine the effect of different environmental stress on growth and development of cotton plants. So, the experiment conducted through a wide range of thermal changes by planting cotton at different dates. This work aimed to performance evaluation of some Egyptian cotton genotypes i.e., Giza 90, Giza 90 x Aust. and Giza 95 under different thermal units related to different planting dates i.e., 1st April, 16th April and 1st May.The results demonstrated that late planting led to decreasing plant height, number of leaves/plant and leaf area/plant. Number of fruiting/plant increased in early planting due to lowered of node of the first sympodium and inducing early balance between vegetative and fruiting. Low temperatures at the beginning of the season and the decrease the number of thermal units in early planting led to increase concentration of chlorophyll a, b and carotenoids in leaves and increase earliness index. Late planting produced the first flower and first open boll in shorter period as compared to early planting, but it consumed more number of heat units. Yield and its quality have increased in early planting where utilized the heat units in producing the highest number of open bolls and enhance cotton fiber properties conversely late planting which used most of the heat units in increasing the vegetative growth. Giza 95 surpassed in all studied characters compared to other genotypes. The efficiency of Egyptian cotton genotypes particularly Giza 95 for use of air thermal units increased in early planting. From the results above, it could be concluded that early planting maximized of the use of heat units by increasing the efficiency use of air thermal units through the growing season which lowered the amount of heat units for necessary production one boll.