The phrase "have had its day" is often used to describe something that is outdated and no longer relevant. To express this sentiment in different ways, one could use synonyms such as "outmoded," "obsolete," "archaic," "old-fashioned," "antiquated," or "deprecated." These words convey a sense of something that has lost its usefulness due to the passage of time or changing circumstances. Other options include "past its prime," "long in the tooth," or "behind the times," all of which suggest a similar idea. Whatever phrase one chooses, the message is clear: it is time to move on from this outdated idea, object, or concept.