When is is carbon dioxide needed by plants to make glucose

Carbon dioxide is needed by pants to make glucose during the daytime when the plants take the available light energy from the sun and convert it into chemical energy which is then used in a process called the Calvin cycle which is a part of photosynthesis that is carried out independent of light but still occurs only during the day.

It is during the Calvin cycle that carbon dioxide together with other compounds is converted into glucose.

It is important to note that the Calvin cycle takes place only during the day and never in the night.