The phrase "calls time" refers to the act of ending a period of activity or work. Antonyms for this phrase could include "beginning," "starting," "instigating," or "initiating." Rather than closing or concluding an event, these words imply the start of a new one. Other antonyms might include terms like "continuing," "resuming," or "extending," which suggest that the activity or work should persist rather than coming to a halt. Depending on the context in which the phrase "calls time" is used, there are a variety of antonyms that could be appropriate to convey the opposite meaning.