Seth MacFarlane - creator and genius behind the show - has stated that episodes take months to make. They are working on many episodes at the same time.
Interesting factoid, in 2001, Seth missed his plane ride from NY to LA due to a night of partying. That missed flight was one of the two planes that destroyed the World Trade Center on Sept. 11, 2001.
I'm an idiot - Seth is FAMILY GUY creator. Trey Parker and Matt Stone do South Park, however the time span is still USUALLY several weeks, but sometimes they REALLY push and get the episode done more quickly. South Park is quicker than Family Guy because the animation is simpler.
Often the creators see that in a month something is going to occur so they begin laying out a story board ahead of time and have most of the episode ready before the movie comes out, and then add a few minutes of show that directly have to do with last minute changes.
K thanks fr the answers I was just wondering cause the new episode had something from the new jackass movie nd it only came out the Friday before the episode aired...
About a week.