  Following Ford et al. (2011, 2012) and Steffen et al. (2012) we derived the
transit timing of 1960 Kepler KOIs using the pre-search data conditioning (PDC)
light curves of the first twelve quarters of the Kepler data. For 721 KOIs with
large enough SNRs, we obtained also the duration and depth of each transit. The
results are presented as a catalog for the community to use. We derived a few
statistics of our results that could be used to indicate significant
variations. Including systems found by previous works, we have found 130 KOIs
that showed highly significant TTVs, and 13 that had short-period TTV
modulations with small amplitudes. We consider two effects that could cause
apparent periodic TTV - the finite sampling of the observations and the
interference with the stellar activity, stellar spots in particular. We briefly
discuss some statistical aspects of our detected TTVs. We show that the TTV
period is correlated with the orbital period of the planet and with the TTV
amplitude.
