The word "untimelier" means something that is inappropriate or at an inconvenient time. Its antonyms are words that describe something that is appropriate or happening at the right time. Some possible antonyms for "untimelier" include timely, punctual, opportune, appropriate, and fitting. These words suggest that something is happening in a way that is well-timed or well-suited to the circumstances. For example, a timely response to an email is one that comes quickly and is relevant to the topic at hand. An opportune moment for a meeting is one that allows all participants to attend and contribute their ideas.