Climate change increases workers' exposure to heat stress. To prevent heat‐related illnesses, according to occupational‐health recommendations, labor capacity must be reduced. However, this preventive measure is expected to be costly, and the costs are likely to rise as the scale and scope of climate change impacts increase over time. Shifting the start of the working day to earlier in the morning could be an effective adaptation measure for avoiding the impacts of labor capacity reduction. However, the plausibility and efficacy of such an intervention have never been quantitatively assessed. Here we investigate whether working time shifts can offset the economic impacts of labor capacity reduction due to climate change. Incorporating a temporally (1 hr) and spatially (0.5° × 0.5°) high‐resolution heat exposure index into an integrated assessment model, we calculated the working time shift necessary to offset labor capacity reduction and economic loss under hypothetical with‐ and without‐realistic‐adaptation scenarios. The results of a normative scenario analysis indicated that a global average shift of 5.7 (4.0–6.1) hours is required, assuming extreme climate conditions in the 2090s. Although a realistic (<3 hr) shift nearly halves the economic cost, a substantial cost corresponding to 1.6% (1.0–2.4%) of global total gross domestic product is expected to remain. In contrast, if stringent climate‐change mitigation is achieved, a realistic shift limits the remaining cost to 0.14% (0.12–0.47%) of global total gross domestic product. Although shifting working time is shown to be effective as an adaptation measure, climate‐change mitigation remains indispensable to minimize the impact.