I don't think there's been a limit in the past, and I can't think of a good reason for one now. (Keep in mind the intent is for interactive fiction only, and for games produced during the month of October.)
Le Grand Guignol has no limit on time taken to create the game, but it's still meant to be for games made starting now-ish, not for that game you've been working on for the last five months, or five years. If you're starting this month that's no problem.
