Phenological regulation is a key determinant of barley adaptation. In South America, late planting often exposes barley to high temperatures, limiting the adaptation of late-flowering European germplasm introduced for yield and malting quality. To investigate phenology and yield-related traits under contrasting environments, a barley population (developed from five elite genotypes) was extensively phenotyped: eighteen traits at four sites, under both normal and late sowing dates over four years. The population was genotyped using the Illumina barley 50K iSelect array. GWAS identified 61 QTL, 43 of which clustered in six hotspots close to PPD-H1 (2H), HvFT2 (3H), Vrn-H3 (7H), and three other regions on chromosomes 1H, 6H and 7H. Phenology did not affect yield on early planting dates, but was negatively correlated to yield on late plantings. Hotspots on 1H and 3H determined yield-related traits on all sowing dates, contributing to yield stability across environments. Hotspots on 6H and 7H affected yield-related and phenological traits only in normal sowing dates, suggesting the potential for increasing yield in optimal environments without penalties in late sowing dates. PPD-H1 affected phenology in late sowing environments, where sensitive alleles (from local parents) shortened phenological phases but did not affect early sowings. The results highlight the importance of phenology on late plantings and suggest that photoperiod sensitivity should provide stability under diverse environments with no trade-off under normal conditions. The lack of crossover interaction of favorable alleles suggests the potential of strategies for combining specific and general adaptation.