Otaku O'Clock

Anime aired from around 11 p.m. until the wee hours of the morning, occasionally indicated by the odd-looking "22:00-27:00" annotation. They are almost universally watched by an older male audience, and often mocked by any shows aired earlier.

This sounds like a rather strange time to broadcast a show that's trying to make money, but it works for several reasons. These kinds of time slots are usually bought by production companies (generally a span of three months, called a cour) who end up as their own sponsor. This is cheaper than depending on someone else's advertising money. These shows have a strong, if unusual, Merchandise-Driven concept that help pay for themselves. This is supplied by the often small but dutiful fan base. The TV station gets to fill an otherwise crappy time slot.

This also creates the infamous tendency to neuter, literally or figuratively, the broadcast in an effort to get you to buy DVDs; recent shows may not even supply the 'full' finale. In fact, many small companies don't even release OAVs anymore unless they've done a TV run, just to make sure their audience wants them. However, how much Fan Service the show actually provides can vary quite a bit.

Interestingly, distribution in the fansub community largely removes this time restriction, as does DVR technology (which allows people to set their TV to record a show at, say, 3 a.m., and then watch it twelve hours later). An unexpected demographic can take interest in a show, or a larger fandom is created for a series that originally had a much smaller one.

See also Watershed, Safe Harbor.

Anime

 * Despite being a Shoujo series, the first season of Mariasama ga Miteru aired at Otaku O'Clock, while the second aired on a more intuitive Sunday morning timeslot. Aside from testing series potential, this was probably a safety device to see how far they were allowed to go and because the producers are well aware of the net created by its Periphery Demographic loyalty. After a "third season" of OVAs, the fourth season again aired at Otaku O'Clock.
 * Soukou no Strain aired around midnight.
 * Macross Frontier was aired at 1:25 AM (rendered on Japanese TV as as 25:25) in spite of having a ridiculous amount of mainstream promotion. This is just one small part of the Noachian deluge of "25" references the series made.
 * Magical Girl Lyrical Nanoha originally showed somewhere around this time, which, considering the otherwise mostly tame content of the show, is the main clue it wasn't originally marketed for little girls.
 * Code Geass' first season aired at 12:30, which apparently allowed them to get away with bloody violence, swearing, The fact that the second season aired at 6 PM on Sunday, a timeslot typically reserved for news programming, required them to drastically alter the plot.
 * Hayate the Combat Butler's first season was on a Sunday morning kids' show time slot, but the second season moved here. Perhaps because of all the references and otaku nature of the show.
 * Last Exile was broadcast at around 1:00 AM during its first run in Japan.
 * Serial Experiments Lain aired at 1:15 AM.
 * According to the Japanese commercials, Gun X Sword appeared at 1:30 AM. Despite this, American audiences frequently tag it as a shonen series.
 * The second season of The World God Only Knows airs around 1 AM or so.
 * Umineko no Naku Koro ni got this sort of time slot when it came out.
 * An early version of Otaku O' Clock relates to different reasons in the years before anime was mainstream in the US. During it's initial 1985-1986 runs, Robotech was shown mostly during the early hours of the morning such as 6:30 or 7:00 am. This was believed to be due to the tendency for parents to still be asleep and unaware of the mature content of what was supposed to be "just a cartoon". It should be noted that Robotech was originally broadcast on NBC and their Saturday Morning Cartoon lineup at the time usually began around 8:00 am. At that time, NBC broadcast an annual primetime preview special giving glimpses into the season's soon-to-start Saturday Morning Cartoon lineup, particularly highlighting new cartoons. Robotech was not mentioned in the fall 1985 special.

Live-Action TV

 * Invisible Girl Ea (Toumei Shoujo Ea) was shown during this timeslot, although it is a live action series (but based on an anime-game). The 22-27 references on Japanese pages to this show did not make sense to this troper until just now.
 * Some Toku programs that are most definitely not for younger audiences also aired during Otaku O'Clock:
 * Garo came on at 1:30 AM, its two-part made-for-TV movie was on at midnight, and its sequel series is set to air at 1:45 AM.
 * Cutey Honey the Live had a 1:00 AM broadcast time.
 * Ultra Seven X was aired at 2:15am on CBC and 2:25am on TBS.
 * Deep Love was shown at "25,30" due to the fact the main character is a prostitute and the audience gets to see her at work.
 * The Ancient Dogoo Girl was on at 1:25 AM and its Dogoon V sequel was on at 1:35 AM.
 * Hikonin Sentai Akibaranger, airs at 1 am and 1:30 am on BS Asahi and TOKYO MX, respectively.

Other

 * In Australia, anime is usually aired at either seven in the morning on a commercial channel (Yu-Gi-Oh!!, Pokémon, Digimon and other kids' programs) or very late at night on the self-styled multicultural channel SBS (the collected works of Hayao Miyazaki, Ghost in the Shell and so forth).
 * .hack//Roots on Cartoon Network fits (or rather, used to fit) this bill, airing pretty close to midnight—though only on one day of the week (Friday), and it eventually got, of course, Screwed by the Network in the middle of the latter half of the anime, giving American fans barely a taste of Haseo's Darker and Edgier prolonged Freak-Out session (aka his forced upgrade into his Flick Reaper form).
 * The short-lived UK channel Anime Central nearer the end of its life consisted of a two-hour block on another channel by the same owners, starting at about 1 AM- on the site for the audience ratings board in the UK (BARB), showings were referred to as "25:00".
 * The Syfy's Ani-Monday block runs from 10PM to 12PM EST. They adjust it for time zones for the standard channel but not the HD channel, so on the west coast you can see it at 7PM, potentially averting the trope.
 * It will be relocated to Tuesdays in January 2011.
 * Logo's "Alien Boot Camp". The website helpfully calls it "where LGBT fans of video games, sci-fi, comics, horror and cool techie stuff collide".
 * This is the theory behind Adult Swim, which airs between 9 PM and 5 AM and devotes its Saturday night broadcast to anime.
 * They've started a new segment called "DVR Theater" which shows some of the older Cult Classic programs around 5 AM.
 * My Little Pony: Friendship Is Magic is a different version of this: episodes aired at 2:30 PM. Because of its popularity of the teen male demographic, considering they have jobs or college, could technically be considered at this. YMMV since it does have reruns (the most notable one being at 6:30 PM everyday, being the only Hub cartoon other than Transformers Prime and Dan Vs.. to air that late.

Fictional Works

 * Chibi Mikusan: In Vocalotown, Black Rock Shooter aired at "25:30".
 * In Lucky Star, Konata is known to lament the fact that shows airing in this slot on normal channels often don't air at all when sports broadcasts run long, in addition to shows airing earlier being bumped into it temporarily.