Posterior TTV predictions of K2-I9b (blue band) and K2-19c (orange band) computed relative to a linear ephemeris (2456813.386969 + 7.9209002 × epoch [BJD_TDB], 2456817.280436 + 11.8983248 × epoch [BJD_TDB] for planet b and c, respectively). We used 1000 random draws from the posterior distribution to estimate the TTV median value and its uncertainty (68.3% CI). In the upper panel, the posterior TTV values are shown and compared with individual transit-time determinations (Appendix B, open and filled error bars). The filled error bars were used as data in the modeling. In the lower panel, the posterior median transit-timing value was subtracted to visualize the uncertainty of the distribution. The posterior median transit time was also subtracted from each observed epoch for the individual transit-time determinations to allow a better comparison with the posterior of the photodynamical modeling.