We have been carrying out a program for over five years to observe transits of selected exoplanets with 1-meter Turkish Telescope, T100 (Baştürk et al. 2014, 2015), by making use of the welle stablished defocusing technique (Southworth et al. 2009) to achieve high photometric precision. Inthis contribution, we review the results of our observing program in timing perspective. The basicidea behind defocusing technique is to have the advantage of posing the detector for longer durations in the observations of bright stars, otherwise observed within very short integration times. Then the effect of the photon noise is diminished, which dominates in the short cadence observations. Longer exposures also help in reducing the noise contribution of the atmospheric scintillation. Noise contributions of the imperfect tracking and flat-fielding are mitigated by integrating over a larger area on the detector as well. Although fewer images can be acquired in a given time, we argue that the timing precision is improved because of better photometric precision. This contribution has been supported by TÜBİTAK-3001 project 116F350.