Dalba & Muirhead (2016) present observations of the third transit of Kepler-421b by the 4.3-meter Discovery Channel Telescope on 19 February 2016. Observations of the third transit show no transit timing variations (TTVs). The lack of TTVs suggests Kepler-421b is either the only planet in its planetary system or the dynamical interactions with unseen planetary companions are too weak to noticeably perturb the orbit of Kepler-421b. Future transits of Kepler-421b will occur on 24 January 2018, 29 December 2019, 2 December 2021, and so on.
Dalba & Muirhead (2016), "No Timing Variations Observed in Third Transit of Snow-Line Exoplanet Kepler-421b", arXiv:1606.09246 [astro-ph.EP]