I’ve spent the past week or so beginning my research into anime timeslots in the mid-to-late 90s, and it’s a truly fascinating subject. My ultimate goal here is to get an accurate accounting of which shows during that period were actually late-night specific, as opposed to just series airing in daytime. In the very tedious and very, very fun process of collecting data on shows airing in this period, I’ve discovered a number of dedicated timeslots that existed around this time that are interesting enough to summarize.
The TV Tokyo Friday 18:30 slot, which lasted for over 20 years, served as a sort of proto-late slot for part of that period. It started rerunning Captain Tsubasa in 1985, but soon moved into rebroadcasting of OVAs and then new anime. Many of the series in this timeslot in the mid-90s are debatably works that would have been OVAs if they had been made 5 years earlier and late-night shows had they been made 5 years later. And that’s not purely idle speculation; Slayers aired in this slot throughout the 90s, but the new Revolution season aired in the same timeslot as Toradora (Wednesdays 25:20, TV Tokyo), and El Hazard had its first TV season aired here (in the same year as the first OVA series) before the second one in 1998 went to a similar late-night slot (Wednesdays 25:15, TV Tokyo).*
The following shows, in order, were broadcast in this slot from 1985-2006:
[First month of airing in square brackets]
Captain Tsubasa (rerun) [1985-05]
Yumemiru Toppo Gigio ’98 (not original slot) [1988-10]
Fushigi no Koala Blinky [1989-01]
NG Knight Ramune & 40 [1990-04]
Starship Troopers (OVA) [1991-01]
Dominion Tank Police (OVA) [1991-03]
Tiny Toon Adventures (American animation) [1991-04]
Salad Juu Yuushi Tomatoman [1992-04]
Tengai Makyou (OVA) [1993-01]
Hello Kitty (2 OVAs in 2 weeks) [1993-02]
Kero Kero Keroppi (3 OVAs in 3 weeks) [1993-02]
Ozanari Dungeon (OVA) [1993-03]
Kenyuu Densetsu Yaiba [1993-04]
Ginga Sengoku Gunyuuden Rai [1994-04]
Slayers [1995-04]
El Hazard: The Wanderers (TV series 1) [1995-10]
Slayers Next [1996-04]
Mahou Shoujo Pretty Sammy [1996-10]
Slayers Try [1997-04]
Battle Athletes Daiundoukai [1997-10]
Lost Universe [1998-04]
Kareshi Kanojo no Jijou (Kare Kano) [1998-10]
Gokudo-kun Manyuuki [1999-04]
Donkey Kong (French animation) [1999-10]
Hamtaro [2000-07]
The timeslot’s animation run ended in 2006-04, when it was replaced with a variety/game show (ロンブーの怪傑!トリックスター). The most interesting stretch is 1995-1999, where they went to Hajime Kanzaka 4 times in 4 April 2-cours, then subbed in Gokudo (a series with a style of comedy similar to that of Slayers).
*Another interesting borderline case is the Rance series. Rance was a straight-up hentai ova in the 90s, but the newly announced Rance 01 may end up being a TV series. It’s director, Takashi Nishikawa, and Seven‘s chief producer, Taku Horie, don’t seem to have any straight hentai on their resumes, at least.
Animetics 
Do you happen to know what happened to TV ratings for Noitamina post-Fractale? Ratings list pre-Fractale are pretty easy to find, but I have a hard time finding anything from 2012 on. Did the timeslot really fell off the tv rankings completely?
Via post 255 in the 2ch ratings archives: http://desktop2ch.tv/iga/1321776520
1.5 1.6 1.7 2.1 2.5 1.5 1.8 2.8 2.0 2.3 2.3 2.5 平均2.05 四畳半/さらい屋
3.4 2.4 2.6 2.3 2.7 2.3 2.6 2.5 2.9 2.0 2.5 終. 平均2.56 もやしもん/屍鬼
2.3 休. 2.2 3.1 2.8 2.7 1.8 2.4 1.6 2.5 2.1 2.7 平均2.38 海月姫/屍鬼
1.9 1.8 1.6 2.1 休. 1.5 2.1 1.9 1.8 1.3 0.9 2.5 平均1.76 フラクタル/放浪息子
1.6 2.5 3.9 2.8 2.5 2.9 2.2 2.0 2.4 2.9 3.2 終. 平均2.62 C/あの花
1.2 2.4 2.1 2.6 2.1 2.5 休. 2.3 1.6 2.4 1.6 2.5 平均2.11 うさぎドロップ/NO.6
2.6 2.4 1.3 2.7 2.6 1.8 2.0 1.9 2.0 1.7 3.0 終. 平均2.18 UNGO/ギルクラ
2.1 2.6 1.8 終. -.- -.- -.- -.- -.- -.- -.- -.- 平均2.16 テルマエ/ギルクラ
1.8 2.3 2.1 1.7 1.4 2.0 2.4 1.5 終. -.- -.- -.- 平均1.90 BRS/ギルクラ
2.6 2.3 2.3 2.1 1.7 1.5 2.1 0.9 1.7 1.5 1.6 2.5 平均1.90 アポロン/つり球
1.8 2.2 2.2 1.2 1.6 1.9 1.8 2.0 1.8 1.3 1.9 終. 平均1.79 もやしもん２/夏雪
2.7 1.8 1.4 1.5 1.8 2.1 2.5 1.6 1.9 2.0 2.0 休. 平均1.93 サイコパス/ロボノ（1クール目）
2.5 1.9 2.2 1.7 1.8 2.3 1.7 1.8 1.9 1.4 2.2 終. 平均1.94 サイコパス/ロボノ（2クール目）
2.7 1.9 2.8 3.0 2.9 2.8 2.1 2.6 2.3 2.5 1.6 1.8 平均2.41 刀語（再）
2.1 1.5 1.9 2.1 1.5 1.4 1.6 1.4 1.4 2.9 1.9 終. 平均1.79 銀の匙（第1期）/あの花（再）
2.6 2.2 2.0 1.4 1.7 1.5 2.1 1.7 1.4 1.3 1.3 終. 平均1.74 ガリドン/サムメンコ
A different stat is given by post 251, but this one corresponds with the older data archived in geocites, and thus, I assume, is better for comparison.
Analysis of the above figures is complicated because Noitamina airs earlier than other late night shows (24:45), but its new shows seem to have continued to dip. For some random TBS Thursday examples, KoiSenChoco averaged a 1.45 at 25:25 in the same season as Moyashimon Returns/Natsuyuki and Amagami SS averaged a 1.72 at 25:29 in the same seasons as the Moyashimon LA/Kuragehime/Shiki combo. Having higher ratings than those two may simply be a function of Noitamina’s retaining some viewer base or just its having an earlier airtime. That and the fact that I have strong personal feelings about what the timeslot has done in the past several years in scrapping any kind of commitment to identity make me a poor judge of what’s actually going on there.