According to Yojoe's summary page it was November, 1985.

http://yojoe.com/comics/joe/joe41.shtml

Many thanks to yojoe for good summary info like this.

This was a nice Hama plot twist that completely goes beyond reality with 24-like time space continuity (amazing that all of that could happen in am hour or two). Bureaucatic relations with State departments of the aforementioned governments would take several months, possibly years. More than ample time for the Joes to KILL everyone living creature on the newly created land mass.

Edit for additional snide comment I couldn't get a driver's license renewed in the time it took them to get sovereignty AND a ceasefire issued.