The word "un-timeliest" refers to something that is not happening at the most appropriate time. Antonyms of un-timeliest can be "timely," "prompt," "punctual," "opportune," "well-timed," "suitable," "convenient," "appropriate," and "seasonable." A timely action or decision implies that it is done at the right time and is beneficial. Prompt and punctual both suggest that the work is finished according to the set time. Well-timed and opportune mean perfect timing, fitting the occasion. Something suitable and convenient is comfortably and aptly done without hindrance. Anything that is appropriate is fitting and proper, while seasonable means the right time of the year.