Antonyms for the phrase "most long-time" can be interpreted in a few different ways. One option is to consider antonyms that describe the opposite of longevity or duration, such as "short-lived," "brief," or "fleeting." Another approach might focus on the quality or intensity of something over time, with potential antonyms including "inconsistent," "sporadic," or "irregular." Additionally, depending on the context in which "most long-time" is used, antonyms might be selected to contrast with or provide an alternative to a specific characteristic, such as "new," "novel," or "experimental." Ultimately, the antonyms chosen will depend on the specific meaning and intent behind the phrase.