If the exchanges are available to trade on 24 hours a day, why is there an open and close session? The futures exchanges need to do a daily maintenance, but why this specific open time? Why cant traders get in a few hours earlier and get the big orders in at different times?
Also, does the entire US market open at 09:30 est? Does anyone know of a website listing the various market times for US, Europe, Asis(my searches keep ending up at the CME) ?

Index futures are tied to the stock markets which do open/close. There are different open/close times for the different cash markets. You have to check but there a couple. Yes, you can trade pre-market. The settlement period is due to both that the cash market closes and so the risk is becomes higher in holding overnight and leverage ratios need to change and because futures expire and need to be settled.

Grantx 

If the exchanges are available to trade on 24 hours a day, why is there an open and close session? The futures exchanges need to do a daily maintenance, but why this specific open time? Why cant traders get in a few hours earlier and get the big orders in at different times? Also, does the entire US market open at 09:30 est? Does anyone know of a website listing the various market times for US, Europe, Asis(my searches keep ending up at the CME) ?

NYMEX, COMEX, CBOE, CBOT and CME exchanges which all trade futures used to be separate but are now all owned by the CME, that's why all your searches end there. The bulk of futures trading is done via the CME but there are other exchanges that trade futures as well.


Futures & Options Trading for Risk Management - CME Group is the go-to website for all that kind of basic information about exchange operning times and so forth.