This paper reports on the results of time resolution measurements of Multigap Resistive Plate Chamber (MRPC). Three 20 gas gaps MRPCs were built with thin float glass sheets and different gap sizes: 160μm, 140μm and 120μm. These chambers have been tested using a different gas flow configurations. The measurements indicate that to reach a better time resolution for small gap size (140μm and 120μm), a smaller gas volume of the chamber is preferable. The efficiency of the chambers in both gas flow configurations has been tested. A time resolution of 25 ps comprehensive of the front-end electronics jitter, with an efficiency of 98% has been achieved for the MRPC with 140μm gas gaps; this is the best time resolution. Moreover, all the chambers have been tested for different particle flux. At the highest particle flux tested, a time resolution better than 60 ps together with an efficiency higher than 80% has been achieved for all the detectors at an instantaneous particle flux of 30 kHz∕cm2. From the efficiency and time resolution study, the rate capability for these three MRPC is similar.