It's actually measured in thousands of years. "Other sources estimate that the time that it takes for a reversal to complete is on average around 7,000 years f

It's actually measured in thousands of years. "Other sources estimate that the time that it takes for a reversal to complete is on average around 7,000 years for the four most recent reversals." A range of 2k-12k is also in the introduction. https://en.wikipedia.org/wiki/Geomagnetic_reversal https://en.wikipedia.org/wiki/Geomagnetic_reversal