A half diallel cross between 8 inbred lines of maize was evaluated under two sowing dates for six quantitative characters in RCBD with three replications. Significant mean squares due to planting date were detected, with high magnitudes in early sowing date compared to those in late one. Genotypes mean squares were significant for all studied traits in both and across sowing dates. Significant mean squares for general (GCA) and specific (SCA) combining ability were obtained in both methods of Griffing (M2 and M4) at early and late sowing dates as well as their combined analysis. Also, the additive (a) and non-additive (b) components were significant for all traits in both and across sowing dates. Mean squares due to interaction between sowing date and both types of combining ability calculated by Griffing method M2 and M4 or (a) and (b) components calculated according to Jones, were significant for number of rows/ear, No. of kernels/row and grain yield/plant. The additive (D) component of Haymans's method was significant only for No. of rows/ear and No. of kernels/row. While, non-additive (H1) component was highly significant for all studied traits in both planting dates. The correlation coefficient between General ( ) and specific ( ) combining ability effects in two methods (Griffing's M2 and M4) was highly significant for all traits. The F test between the methods used in this study revealed that Griffing's methods (M2 and M4) and method of Jones reached similar estimates for additive, non-additive and error variances in the traits under study. While, the method of Hayman gave different results compared to other methods of analysis in some traits. The correlation coefficients of additive, non-additive and error mean squares derived from four methods for all traits in both and across planting dates were highly significant, indicating the strong relation between these four methods in estimating additive, non-additive and error variances.