Context : In the time-ordered data ( TOD ) files of the Wilkinson Microwave Anisotropy Probe ( WMAP ) observations of the cosmic microwave background ( CMB ) , there is an undocumented timing offset of -25.6 ms between the spacecraft attitude and radio flux density timestamps in the Meta and Science Data Tables , respectively .
If the offset induced an error during calibration of the raw TOD , then estimates of the WMAP CMB quadrupole might be substantially in error .

Aims : A timing error during calibration would not only induce an artificial quadrupole-like signal in the mean sky map , it would also add variance per pixel .
This variance would be present in the calibrated TOD .
Low-resolution map-making as a function of timing offset should show a minimum variance for the correct timing offset .

Methods : Three years of the calibrated , filtered WMAP 3-year TOD are compiled into sky maps at HEALPix resolution N _ { \mathrm { side } } = 8 , individually for each of the K , Ka , Q , V and W band differencing assemblies ( DA ’ s ) , as a function of timing offset .
The median per map of the temperature fluctuation variance per pixel is calculated and minimised against timing offset .

Results : Minima are clearly present .
The timing offsets that minimise the median variance are -38 \pm 8 ms ( K , Ka ) , -27 \pm 3 ms ( Q ) , -43 \pm 8 ms ( V ) , and -47 \pm 194 ms ( W ) , i.e .
an average of -30 \pm 3 ms , where the WMAP collaboration ’ s preferred offset is 0 \pm 1.7 ms. A non-parametric bootstrap analysis rejects the latter at a significance of 99.999 \% .
The hypothesis of a -25.6 ms offset , suggested by Liu , Xiong & Li from the TOD file timing offset , is consistent with these minima .

Conclusions : It is difficult to avoid the conclusion that the WMAP calibrated TOD and inferred maps are wrongly calibrated .
CMB quadrupole estimates ( 3 / \pi ) C _ { 2 } based on the incorrectly calibrated TOD are overestimated by roughly 64 \pm 6 \% ( KQ85 mask ) to 94 \pm 10 \% ( KQ75 mask ) .
Ideally , the WMAP map-making pipelines should be redone starting from the uncalibrated TOD and using the -25.6 ms timing offset correction .