It won't be long before he comes.

0A: It will be a long time before he comes.02br
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00B: It won't be long before he comes.02br
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00Why in B can't we use "a long time" instead of "long"?02br
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00I think the adverb "long" is used mainly in contexts expressing Negative situations. 02br
00But how about "a long time"?02br
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00Is "a long time" used in contexts expressing that something with definite amount or degree surely exits?0-