Yes, plants emit CO2 day and night. CO2 is an end product of metabolism which is the burning or oxydation of sugar that occurs in the mitocondria.
The Calvin cycle of photosynthesis can occur only in light or in daytime,if you wish. However the intake of CO2 varies across species. CAM species, of which jade (crassula ovata) is an example, take in CO2 at night and store it in malic acid. This means the stomata can be closed during the heat of the day, but the Calvin cycle can operate, unlike the common C3 species that have no means of storing CO2 and must take in CO2 during daylight as well. The third type, C4 also utilizes metabolism of malic or aspertic. Maize and sugar cane are expamples of C4 plants.
The critical piece of carbon fixation is an enzyme known as RuBisCo (an acronym for a very lengthy chemical name). RuBisCo does the actual fixing of carbon into elemental sugar. I also sometimes incorporates oxygen instead. The rate of fixation increases with temperature, however, the rate of fixing oxygen increases more rapidly than that of fixing carbon so that at temperatures near 95F (35C) and above, there is no net carbon fixing. Malic/aspertic acid in C4 and CAM plants is a mechanism of effectively blocking oxygen from RUBISCO and so allows carbon fixation to occur at higher temperatures. Hence, these are typically tropical species.
So plants continually emit CO2 because of the process of life. They emit more the hotter the environment, so this goes up and down though the course of a day. Carbon fixation occurs only via photosynthesis. Most species are C3 and will release more oxygen than carbon dioxide during the daylight hours and while the temperature is below 95F (35C). The same for C4 plants, except that there will continue to be a net fixation of carbon at yet higher temperatures. CAM, plants, however, will take in carbon at night.
SHORT VERSION: you are correct, but for plants such as crassula ovata and pineapple.