Defining the Early, Mid, and Late Segments of a Decade

Early: Years ending in 0 through 4

Mid: Years ending in 5 and 6

Late: Years ending in 7 through 9
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How would I define the early, mid and late segments of a century or even a millennium?

Century:
Early: years ending in 0 and/or 1 through 49 (so, early Nineteenth Century: 1800/1801 through 1849)
Mid: 50 through 69
Late: 70 through 99

Millennium:
Early: years 0 and/or 1 through 499
Mid: years 500 through 699
Late: 700 through 999
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In any case, we are ensconced in the late aughts. More later.