In the sentence, "Let’s not waste any more time, let’s go and buy it," the phrase "any more time" means additional time or extra time. It implies that some time has already been spent or wasted, and the speaker is suggesting they shouldn’t spend even one more moment on it.
This is slightly different from "Let’s not waste our time," which would mean that they don’t want to waste their time in general. "Any more time" specifically emphasizes stopping now, to avoid spending additional time.
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