Sad but true.
>magnetic field reversals do NOT happen at regular intervals
When the Earth's magnetic field reverses, a new stripe, with the new polarity, begins. Such magnetic patterns led to recognition of the occurrence of sea-floor spreading, and they remain some of the strongest evidence for the theory of plate tectonics.
https://oceanexplorer.noaa.gov/edu/learning/2_midocean_ridges/activities/seafloor_spreading.html
Go back to class.