The word "un-timelier" means not suitable or badly timed. Its antonyms are timely, opportune, well-timed, and favorable. Timely means happening at the right moment or season. Opportune means occurring at a moment that is suitable or advantageous. Well-timed means being at the right time, neither too early nor too late. Favorable means advantageous or beneficial to the progress or development of something. Using any of these antonyms of "un-timelier" would convey the opposite meaning and suggest the right time or appropriateness of a given situation thus making communication more effective.