Among time-resolved studies of compact binaries, systems including white-dwarfs are particularly challenging due to their faintness and to the short duration of the eclipses. The 2.4m Thai National Telescope (TNT) equipped with ULTRASPEC is an ideal facility for such investigations, due to a combination of sensitivity and relatively long instrument allocations. We report our work on the newly found eclipsing post common envelope binaries (PCEB) from the Catalina Sky Survey (CSS). PCEBs consist of white dwarf star with a low mass companion. While most of PCEBs usually have short orbital periods of a few hours, some systems are found to be in long (>1 day) period. In this work, we focus on PCEB with orbit period ～less than 0.5 day. To select the system, we create the light curve of all PCEB in the CSS data and calculate the orbital phase for all these binaries. Then we choose the systems with prominent eclipses for our follow up observations. We obtain the light curve of four systems with 2.4m TNT. However we see the primary eclipse only in two systems, J0500+1431 and J0738+2855, while in another system, J2234+2456 we get only partial eclipse. Next, the time of the mid—eclipse using several methods (e.g. kwee van woerden and least square) will be calculated. Moreover the new ephemerides for these systems will be provided.