"Called a day" is a phrase typically used to indicate the end of something, whether it be work or an activity. Some antonyms for this expression could be "beginning a day" or "launching a project". Instead of ending something, these phrases suggest a fresh start or a new beginning. Other antonyms could include "continuing on", "carrying on", or "sustaining momentum", implying that the work or activity is not yet finished and there is more to be done. Alternatively, "pausing for the night" or "temporarily closing a chapter" suggest a temporary end, with the potential to pick up where one left off.