Nanex ~ 31-Aug-2012 ~ SPY Close AnomalyThis is an update to charts published last week which showed how about 2 seconds worth of trades and quotes in SPY were jammed into the last millisecond of the day.
When looking at condition fields of each trade around the close in SPY on August 31, 2012, we noticed something that doesn't add up, and it has to do with when trades first appear with the Form-T condition. Form-T is a condition used to notify traders if the trade was executed before or after regular market hours. Trade reports using the Form-T trade condition first appear from the BATS exchange immediately after 16:00:00. This is normal and expected behavior (if there are no delays). However, Form-T trades from Nasdaq and NY-ARCA do not appear until over 1 full second after market close. After many "regular" trades occur. Since we know that everything was delayed at the close, this too makes sense: it is further confirmation of how delayed things where at that time.
However, trades and quotes from BATS appear to line up (more or less) with trades and quotes from Nasdaq and NY-ARCA. So why do trades from BATS show Form-T trades right away, as if there is no delay? Our best guess is that mechanism that sets the Form-T condition is not the same for all exchanges, and those trades from BATS should not have been marked Form-T.
The charts below also illustrate the fact that quote and trade timestamps do not accurately reflect when the quote or trade actually occurred. This is because trades and quotes are timestamped right before transmission, which effectively hides all delays up until that point.