This also suggests that you should really restrict your investment times to moments when conditions are very very favorable. Doesn't it say that "time in the market" is really not the driver of returns? If 0.41% of time can have such a massive impact then there must be lots of times where you could simply sit in cash and not miss much of the return.

You need a few hallmarks to have a sense of which is which, but is it really so difficult? For instance, bad weeks tend to cluster together much more so than good weeks. Avoiding bad weeks might not be so difficult. Probably some simple macro calls based on credit conditions. This data suggests you don't have to time it too carefully, since a few trading days carry so much impact, once it is clear that credit is being offered on silly terms. Sit out the game until the chickens come home to roost.