"Calling it a day" is an idiom that means to stop working or pursuing a particular task for the time being. Some antonyms for this phrase could be "continuing on," "persevering," "persisting," or "staying the course." These words all suggest a desire to keep working or pursuing a task further, rather than stopping or abandoning it. Other antonyms might include "starting fresh," "beginning again," or "renewing efforts," since these phrases all suggest a desire to restart or re-energize a project that may have been paused or abandoned before. Ultimately, the antonym for "calling it a day" will depend on the context in which it is used and the specific goals or objectives at hand.