Discrete correlation functions (DCF) as functions of time lags τ between the 1.3-mm and 3-mm lightcurves (see Fig. 1) of each AGN. The black graphs indicate the measured DCF, bin sizes Δτ are indicated in the corresponding diagrams. The maxima of the curves correspond to the most probable time lag between the spectral bands. Grey shaded areas mark the DCF ranges  [max(DCF),max(DCF) − 3σ]  with σ being the statistical error of max(DCF). Thus all values located within the shaded area are consistent with the maximum of the DCF curve within 3σ confidence. A positive (negative) time lag means that the 3-mm lightcurve preceeds (lags behind) the 1.3-mm lightcurve. Vertical dashed lines mark the null positions of the time lag axes, corresponding to the absence of time lags.