SHJ
If you say your bags will be checked through then I take it your onward destination is a country outside the USA?
If not then you will have to claim all your bags and go through immigration and then recheck those in for your onward flight...
If you have 9 hours layover then of course you can clear air-side, and spend your time outside the airport if you wish then come back later to fly on...
It is no problem to leave the airport as long as you clear out in the normal way (ESTA needed)