Daily noise blocks do not resolve an optical pulse period change between FO Aquarii's 2021 and 2025 TESS visits

We test the optical pulse period difference between the 2021 and 2025 TESS visits to FO Aquarii. This work builds on an SCI pulse amplitude study that reported both fitted periods. We repeat the common fits from public 120-second light curves. We add a period contrast with errors from daily noise blocks. The period in 2025 minus the period in 2021 is -0.00947 second. The approximate 95% interval is -0.02175 to +0.00280 second. An interval that treats each residual as independent excludes zero. Block lengths from half a day to four days give intervals that include zero. New fits let the spin, beat, and spin-minus-two-orbit peaks have separate clocks. Their intervals also include zero. A conditional residual-sign experiment and numerical recovery checks support the local calculation. The result does not resolve a period change under the tested pulse and noise models. It does not prove a constant period or identify a stellar torque. The package preserves raw data, provenance, source code, covariance matrices, figures, and instructions for repetition.

FO Aquarii · TESS · intermediate polar · optical pulse timing · correlated noise · period uncertainty · reproducible analysis