Maize grain yield greatly reduces when subjected to heat stress around flowering and early grain filling, but the responses of temperate (Te) and tropical (Tr) maize genotypes to heat are unclear. For this, 162 maize inbred lines with Te, Tr and Te×Tr were grown at six sowing dates over four years of 2015 – 2018. Yield reduction was mainly a function of low kernel number under heat stress. Kernel number on average reduced by 73-98% under heat stress around flowering, with Tr inbred lines having significantly smaller reductions than Te and Te×Tr inbred lines. Kernel number reduction of Te, Tr, and Te×Tr varied largely in heat stress, indicating there are both heat sensitive and tolerant inbred lines in each group. Tr inbred lines on average maintained a lower flowering – time plasticity than Te inbred lines. Post-silking growth in a short period of approximately two weeks were most sensitive to heat. Adjusting sowing date was a more effective strategy to reduce heat impacts around flowering than genotypes, but sowing date and genotype combined together only alleviated ~80% of negative effects of heat stress on yield. Heat tolerant inbred lines used in this study can be potential germplasm resource.