_if_ this actually holds... (1) "overnight" is longer than intraday: the NYSE on which AIG is traded is only open for 27% of the day (930-1600). That's not enou

_if_ this actually holds... (1) "overnight" is longer than intraday: the NYSE on which AIG is traded is only open for 27% of the day (930-1600). That's not enough to explain the effect, though. (2) many (most?) large companies announce financial results after market close. Assuming that's one of the long-term drivers of change, it makes sense there's more net movement when you include those.