Kepler Q1 to Q17 phases of KIC 5520878 do not support a common delay in local two-mode fits

We test whether a smooth common time delay can explain the phases of the known primary and secondary pulsations of KIC 5520878. We fit Kepler release 25 quarters 1 to 17. With 20-day fits, local time-delay steps differ by 810 seconds RMS in raw flux and 827 seconds in corrected flux. The primary steps alone have RMS values of 30 and 33 seconds. The mismatch persists with 10-day and 30-day fits and in two time subsets. A coherent sampling-matched signal recovers a shared delay. Local residual controls test conditional recovery. The result does not support orbital light travel time as the sole cause of the phase changes. It does not exclude a smaller common delay or identify the cause of the mode-specific changes. The flux products share exposures, and no independent instrument confirmation is available. This is an exploratory follow-up to known variable pulsations, not a new planet or signal detection.

Kepler · KIC 5520878 · RR Lyrae · phase modulation · light travel time · pulsation timing