A field experiment was carried out during the summer seasons of 2015 and 2016 in clay loamy soil of ICAR Research Complex for Eastern Region, Patna to study the phenology, accumulation of growing degree days (GDD), heliothermal units (HTU), heat use efficiency (HUE), heliothermal use efficiency (HTUE) and performance of five sorghum cultivars including 3 hybrids (CSH 13 ,CSH16 and CSH 30) and 2 varieties (CSV 23 and SPV 462) were grown under two sowing dates viz.16th February and 3 rd March in split-plot design. For our study purpose and as per package of practices, February 16 is considered as early sowing and March 3 as timely sowing condition. It was observed that GDDs and HTU reduced significantly by 45.9 oC days and 663.6 oC days hr respectively, in early sowing. The sorghum cultivars SPV 462 and CSH 13 accumulated markedly higher GDDs and HTUs. On mean basis, cv. CSH 16 produced significantly higher grain yield (5.51 tha-1) followed by CSH 13 (4.93 t ha-1). The significant reduction in grain yield was recorded in earlier sowing date than the timely sown crop. The phenothermal index gradually increases from emergence to maturity in all the tested cultivars irrespective of sowing date. Sorghum hybrid CSH 16 showed better performance in terms of HUE and HTUE followed by CSH 13 and SPV 462. Varieties giving higher yield, HUE and HTUE are identified under the varying growing environments, so as to suggest the appropriate sowing time of sorghum cultivars in middle the middle Indo-Gangetic Plains.