  Currently the only technique sensitive to Earth mass planets around nearby
stars (that are too close for microlensing) is the monitoring of the transit
time variations of the transiting extrasolar planets. We search for additional
planets in the systems of the hot Neptune GJ 436b, and the hot-Jupiter XO-1b,
using high cadence observations in the J and Ks bands. New high-precision
transit timing measurements are reported: GJ 436b Tc = 2454238.47898 \pm
0.00046 HJD; XO-1b Tc(A) = 2454218.83331 \pm 0.00114 HJD, Tc(B) = 2454222.77539
\pm 0.00036 HJD, Tc(C) = 2454222.77597 \pm 0.00039 HJD, Tc(D) = 2454226.71769
\pm 0.00034 HJD, and they were used to derive new ephemeris. We also determined
depths for these transits. No statistically significant timing deviations were
detected. We demonstrate that the high cadence ground based near-infrared
observations are successful in constraining the mean transit time to ~30 sec.,
and are a viable alternative to space missions.
