The challenge is twofold:
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As pointed out, starting date is important
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DCA is a simplistic method which ignores the rate of change in either direction
Everyone would like to “buy low and sell high”, but the while concept of this strategy is to hold forever.
Assuming the stock market is cyclical - even if those cycles are a decade or more long, understanding that it is worth more to invest as the price of an equity moves towards and then below the mean, than when it is rising from its mean value, the question is more about where to park money when the trajectory is in the wrong direction than it is about how to divide the lump into twelve piles.
This is more about putting your thumb on the scale than it is about market timing.
Jeff