Time in market > timing the market.

I've heard of the changes to the NASDAQ rules and I somewhat get how they make it so these stocks are included in index funds earlier than before. As far as I know, NYSE and others haven't done the same change so index funds there are "safe", i.e. will include the stocks only after a longer period, implying that it will have settled in value by then. Is that true at all? I'm sure the situation is much more complicated, but I do wonder how to figure out how much I'm affected.