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How much does scheduling a daily batch by historical grid intensity help when computing capacity and idle power are explicit? We evaluate seasonal clock-time profiles trained on 2023 public Great Britain data, with equal work and equal energy in every comparison. At 50% utilization, assigned carbon falls by 11.63% in 2024 and 12.81% in 2025 relative to uniform processing. Setting idle power to 50% of maximum power reduces these advantages to 3.88% and 4.27%. Some dates have higher assigned carbon after shifting. These results describe a fixed historical workload benchmark and an accounting signal; they do not measure avoided emissions.

• Published, Reproduced, Reviewed.Published, Reproduced, Reviewed: In the frozen Great Britain daily-batch benchmark, seasonal profiles trained on 2023 data reduce assigned carbon versus uniform processing by 11.63% and 12.81% at 50% utilization with zero idle power in 2024 and 2025, but by 3.88% and 4.27% when idle power is 50% of maximum; at 87.5% utilization with zero idle power the reductions are 3.37% and 3.64%, while the half-utilization policy increases assigned carbon on 16 of 364 and 10 of 365 evaluation dates, respectively, conditional on the specified processor model and estimated average intensity data.

Do historical electricity schedules help when jobs arrive throughout the day and cannot wait indefinitely? We evaluated fixed seasonal profiles and recent-history profiles on public Great Britain grid records. For the primary workload, seasonal scheduling lowered mean assigned carbon intensity by 11.24% in 2024 and 12.01% in 2025 relative to immediate execution. Yet 17.61% and 15.55% of jobs received higher intensity. Recent-minus-seasonal mean differences were -0.21 and -0.07 g CO2/kWh. These are retrospective accounting results for a synthetic workload, not measured emissions avoided.

• Published, Reproduced, Reviewed.Published, Reproduced, Reviewed: Conditional on the frozen Great Britain national intensity snapshot and a uniform half-hour arrival workload, three-hour jobs allowed up to six hours of start delay have 11.24% and 12.01% lower mean assigned intensity under 2023-trained seasonal profiles than immediate execution across 17,424 and 17,472 jobs in 2024 and 2025, respectively, while 17.61% and 15.55% have higher intensity and a lagged recent-history profile changes the seasonal mean by -0.21 and -0.07 g CO2/kWh, without establishing causal emissions avoided or future workload performance.

Can a simple electricity-use schedule transfer across years? We selected seasonal three-hour windows using 2023 data and evaluated them in later Great Britain grid records. Relative to midnight use, assigned average carbon intensity was 5.78% lower in 2024 and 13.15% lower in 2025. The schedule performed worse on 137 and 111 days, respectively. A single year-round window did not improve both years. These retrospective accounting results describe the recorded grid; they do not estimate emissions avoided by changing electricity demand.

• Published, Reproduced, Reviewed.Published, Reproduced, Reviewed: In the frozen Great Britain national Carbon Intensity API actual series, three-hour seasonal UTC windows selected only from 2023 yield mean assigned-intensity reductions versus 00:00-03:00 UTC of 5.778479% across 364 complete days in 2024 and 13.150070% across 365 days in 2025, compared with -9.430428% and 2.353958% for the single 2023-selected year-round window, while the seasonal rule is worse on 137 and 111 days respectively; these are finite-period accounting comparisons and do not estimate causal emissions reductions.