The amount of CO2 the plants give off at night is very small. The idea that it is not safe to be around plants at night is an old wives tale. My grandmother used to believe that, and would not sleep in a room with plants because of it. Even as a child, I realized that if there was a fly or cockroach in the room it was probably giving off more CO2 than all the plants she might have had in the room. Please feel free to walk in the park or a forest for that matter at night. If there is a squirrel in the trees it is probably giving off more CO2 than all the trees in the park.
I should also point out that CO2 spreads out very quickly in the air, due to simple diffusion, not to mention wind. The CO2 in the park spreads out so rapidly that the concentration of CO2 in the park is not detectably different from the CO2 level blocks away at your home.