The phrase "hast at it" suggests a sense of urgency or haste, implying that action should be taken quickly. Its antonyms, on the other hand, involve words that suggest taking one's time or proceeding slowly. Some of the antonyms for "hast at it" might include words such as delay, hesitate, procrastinate, dawdle, or drag one's feet. These words imply a sense of caution, perhaps suggesting that it is better to take one's time to consider options before making a decision. Ultimately, whether to "hast at it" or proceed more slowly depends on the situation and context, as well as the individual's personal style and preferences.