This study was conducted to assess the influence of varying agronomic management on rice crop phenology using different agro-meteorological indices viz., accumulated growing degree days (GDD), photo thermal units (PTU), and heliothermal units (HTU). Further, heat use efficiency (HUE) was also calculated to check the change in the amount of dry mass. The rice variety ‘Hasanta’ was grown under varying transplanting dates viz., 10, 20, 30 July, and 10 August with nitrogen (N) levels as recommended N level (N100), 25% lower (N75), and 25% higher (N125) during the field experiments for two years. Results showed that the earlier transplanting date 10 July with N125 produced a maximum grain yield of 4443, 4510 kg/ha which was at par with planting on 10, 20, and 30 July for both years the with application of either N125 or N100. Moreover, the transplanting date of 10 July in both years took maximum of calendar days to attain different phenological stages till physiological maturity (143.74 and 143.65 days), while the same effect was reduced significantly with subsequent delay in transplanting with higher values of GDD (2677.2 and 2810.5), HTU (13,531 and 13,975°day hours), and PTU (417,923, 36,290°day hours) respectively for maturity stage in both years. Further, HUE was found to be highest for the transplanting date of 10 July, followed by 20, 30 July, and 10 August. The varieties exhibited a decrease in the necessary heat units to achieve various phenological stages with the postponement of the transplanting date.