The CME says that Globex halts trading at 10:30 a.m. CST on Monday. That seems to imply that it's open from Sunday night till Monday morning: http://www.cme.com/trd/calhrs/2004_mlkday825.html
One more thing, the CME considers Sunday Night through Tuesday's close as one trade date- Jan 20th. So while, Globex halts on Monday morning, it reopens on Monday evening and orders placed on the system on Sunday or Monday will work through Tuesdays close.