12
Superman first appeared in Action Comics #1, dated June 1938. Batman debuted in Detective Comics #27, the May 1939 issue, eleven months later. You didn't ask, but Robin first appeared in Detective Comics #38, dated April 1940 -- eleven months after Batman.
One but Batman made his first appearance in May 1939 in Detective Comics #27and Superman made his first appearance June 1938 in Action Comics #1 so really eleven
The first live-action film about both Superman and Batman will happen in the sequel to "Man of Steel" which is coming to theaters on May 6, 2016 (after the original release date of July 17, 2015 was pushed up 10 months).
There were 2 early 1940's serials - 1943 was Lewis Wilson (Note: this serial was re-released in 1965 a few months before the Adam West Batman made it's debut). 1949 was Robert Lowery
Movies usually take about a year just for the behind the scenes things, such as writing and casting, and then anywhere from a couple of months to about six months for the filming, plus another couple of months for CG.
Ten Months was created in 2001.
January is 9 months before October.
Nine Months was created on 1995-07-14.
Twelve Angry Months was created in 2007.
Six Months in Mexico was created in 1888.
A Thousand Months was created on 2003-05-16.
September is two months before November.