Do they usually film the entire season the spring or summer before and then release them from the can weekly, or do they film it on a weekly basis shortly before the episodes actually air? For example, ALF’s last episode aired in March 1990 - do you think it’s more likely it was filmed just that February or in the summer of 1989?
I imagine it depends on the show, but I get the idea that most sitcoms are filmed only a couple weeks to a couple months before they’re aired, while more complex shows like Lost and Breaking Bad I’d imagine are filmed a lot further in advance.
Studio audience sitcoms are filmed on a weekly schedule, typically about two months prior to airing to allow sufficient time for post-production tasks. The production will take breaks to coincide with the broadcast schedule hiatuses. Sometimes exceptions occur, such as when a whole season ends up in the can to be dumped at an accelerated schedule over the summer or as a midseason replacement.
Single-camera shows may require a lot more post-production time and some episodes may take more or less than a week to shoot, depending on requirements.
Dramas are also shot on the same schedule as sitcoms. This often causes trouble on shows. If the shooting schedule goes beyond five days, a sitcom schedule, then they run into real deadline problems.
This has its roots in history. When the networks were the whole TV world, all the production companies geared their schedules to coincide so that actors, writers, directors, and producers could move on at the end of a season.
Cable shows now run on different schedules, and they also normally have shorter seasons. So they can be fully shot before airing. Mad Men, e.g., split its final season into two seven-episode seasons and all the episodes were finished before airing. So when it winds up in a couple of months, you’ll be seeing what was done last year.
That’s much more like British television. They often have six- or even three-show seasons, and those are all complete before airing.
Filming will start in July, for beginning to air in September. Both these dates vary, but broadly that’s the way it goes.
For sitcoms*, they have a regular schedule that fits within a week, but they do take hiatuses off for writing to catch up, so what often happens is by the time they reach their Xmas hiatus, instead of being 10 weeks ahead of broadcast, they’re now only six weeks.
They will resume shooting in the second week of January, and will have two or three episodes in the can, from filming in the previous December, to broadcast from mid-to-late January. Interruptions like Awards shows and the Superbowl will give them more catch-up time, but by the final episode of the season, usually in March, there may only be three or four weeks between shooting and broadcast.
*Hour-longs take way longer to shoot, maybe as much as two weeks per ep, so they can get caught up quite rapidly. A shorter season of 16 episodes can be a blessing for that reason.
The hour dramas I worked on usually finished shooting the last show of the season in late April, to air mid-to-late May. Network TV shows tend to fall behind schedule for a variety of reasons, and scramble to keep up towards season’s end.
Filming of the original Star Trek shows (I know, not everyone would call that a sit-com) sometimes went right down to the wire, or worse. This was discussed in The Making of Star Trek.
They got so much in a bind to get some shows out on time that they took a relaxing breather to give them a chance to get caught up: They chopped up the original pilot episode, spliced the pieces together with some tid-bits of new filming, and came up with the two-episode The Menagerie Parts I and II. According to the book, that is why they did that.
South Park, famously, starts each episode from scratch as soon as the previous one airs. There’s an amazing documentary 6 days to air about the intense process of a South Park episode from start to finish. However, it stands as an extreme outlier. The Simpsons, by contrast, take 6 - 8 months to make each episode and have multiple running in parallel at all times.