Electrical discharges are increasingly used to dissociate CO2 in CO and O-2. This reaction is the first step in the way for the synthesis of value-added compounds from CO2 by using renewable electricity. If efficient, this technology might allow at the same time recycling CO2 and storing renewable energy in chemical form. At present, while the dissociation degree is measured in the reactor exhaust, little is experimentally known about the dissociation kinetics in the discharge and post-discharge. This knowledge is however critical to increasing the overall efficiency of the plasma process. To estimate the time dependence of the CO2 dissociation following a discharge event, we have coupled a LIF diagnostics to a nanosecond repetitively pulsed discharge in a mixture of CO2 and H2O. This paper discusses a procedure to obtain data on the time evolution of the CO2 dissociation, its limits and future perspectives. In addition, the local gas temperature is measured as well. We find that a few microseconds after the discharge pulse, CO2 is highly dissociated with a temperature around 2500 K. In about 100 A mu s, the temperature decreases at about 1500 K while the dissociation is reduced by about a factor of three.