Quote from traderum:
Hmm. yes the calculation gives a total of only 16 hours/day,
but my experience via the broker IB is 23.5 hours/day.
There is only a half hour window where the system disconnects the client
and doesn't allow login for 30 minutes (23:50 - 00:20 ET).
As stated in the wiki article, Extended hours trading mostly happens
on the ECNs, these electronic markets independent of the regular NYSE/NASDAQ/AMEX/CME markets.
Hmm. I can't confirm this. They trade together with the stocks. Having
a stock trading, but its option not trading is IMHO an impossible situation
with far reaching consequences...