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Well the notion was, the strict boundaries that would or would not include ophiucus, the ecliptic only clips it, so more like a hundred years.
Edit: "Based on the 1930 IAU constellation boundaries, suggestions that "there are really 13 astrological signs" because "the Sun is in the sign of Ophiuchus" between November 30 and December 18 have been published since at least the 1970s.[5]"
50-90 years according to wikipedia
Backstop
Well they were invented by the Babylonians, so roughly 35000 years.