Transit times of KOI-1257.01 compared to the best linear ephemeris found in Model C (dashed line). The grey regions represent the 63.8%, 95.5%, and 99.7% confidence regions of the best linear ephemeris (from dark to light grey). The confidence regions account for the covariance between the orbital period and the epoch of first transit, but this covariance is too small to be visible in this plot.