The antonyms for the word "most timesaving" are numerous. Instead of being efficient and saving time, an action or method could be inefficient and time-consuming. Some antonyms include slow, wasteful, sluggish, delayed, and tedious. Activities that are not streamlined could be considered lengthy and complicated. Instead of being productive and efficient, they can take a lot of time and effort. Other antonyms for "most timesaving" could be nonsensical, counterproductive, useless, and unprofitable. In conclusion, there are many words that can be used as an antonym for "most timesaving," depending on the context and meaning of the sentence.