  A large fraction of the previously estimated WMAP CMB quadrupole signal would
be an artefact of incorrect Doppler dipole subtraction if the hypothesis of a
small timing interpolation error were correct. Observations of bright
foreground objects constitute part of the time-ordered-data (TOD). Scans of an
object in different directions should be shifted by the would-be timing error,
causing a blurring effect. Three half-years of the calibrated, filtered WMAP
TOD are compiled individually for the four W band differencing assemblies
(DA's), with no masking of bright objects, giving 12 maps for each timing
offset. Percentiles of the temperature-fluctuation distribution in each map at
HEALPix resolution N_side=2048 are used to determine the dependence of all-sky
image sharpness on the timing offset. In the W band, the 99.999% percentile,
i.e. the temperature fluctuation in the approx 503-rd brightest pixel, is the
least noisy percentile. Using this statistic, the hypothesis that a -25.6 ms
offset relative to the timing adopted by the WMAP collaboration gives a focus
at least as sharp as the uncorrected timing is rejected at 4.6\sigma
significance. The Q and V band maps also reject the -25.6 ms offset hypothesis
at high statistical significance. The requirement that the correct choice of
timing offset must maximise image sharpness implies that the hypothesis of a
timing error in the WMAP collaboration's compilation of the WMAP calibrated,
filtered TOD is rejected at high statistical significance in each of the Q, V
and W wavebands. However, the hypothesis that a timing error was applied during
calibration of the raw TOD, leading to a dipole-induced difference signal, is
not excluded by this method.
