Stock Markets Exposed

Are Electronic Communications Networks / ECNs for Stock Market open 24/7 or is there times when they r closed?

I am looking at GM stock charts on Nasdaq after hours but it does not show the date . I am thinking the chart is showing Wednesdays data since normal trading ended early plus it likely was closed for Christmas. I will propbably have to wait for Pre-Market data. Is there other times when institutional investors do not have access to ECNs?

Public Comments

1. The only time you have real live data is when the markets are open and even then if you are using a broker or "on line" access system to do your own trading there tends to be a slight lag time in the numbers you have vs. the numbers that are actually at the exchange real time. the lag can be slight ~ meaning seconds. However, sometimes seconds can mean a lot. People can use their on line privileges to set up trades they wish ~ those trades will only come on line when the markets open or specifically when the trader has set up the parameters for a trade to happen at a particular price point.
2. No they are not open 24/7. For example Nasdaq extended trading is 8:00-9:30 AM Eastern Time and 4:00-6:30 PM Eastern Time.