The word "most elapsed" refers to the amount of time that has passed in a certain situation. Some antonyms for this phrase could be "least elapsed," "shortest duration," "minimal time," or "least amount of time passed." These antonyms imply a shorter period of time that has passed, which could be viewed as positive or negative based on the context. For example, in a boring meeting, you may wish for the time to pass quickly and hope for the "least elapsed" time possible. However, when enjoying a vacation, you would want the "most elapsed" time possible to make the most of it.