I think maybe it should also be noted that only posting +1 is against the community rules. It's fine to post +1 and then continue with an explanation or further advice, just not '+1' or something like that which does not contribute to the thread.
As far as the rep question- I don't think it matters how long it's been, it matters how many other people you give it to. This prevents people from continually giving the same person rep over and over again.
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