By market:
In Greenville-Spartanburg-Asheville WYFF was definitely the first by around 1987 or 88 (possibly earlier than that, with airing CNN Headline News and NBC Overnight News in late-night/early-morning). I'm unsure of the exact year. No other stations were 24/7 after that until WSPA in the Summer of 1995, when they were burning off Golden Girls reruns late Friday nights and airing syndicated first-run shows late Saturday nights. Also, WLOS signed off every night until ABC World News Now premiered in early 1992. WHNS began 24/6 operations for good by Fall 1988 (still signing off every Sunday night around Midnight-1 a.m. well into almost the late 90's); they were the last to go complete 24/7 in Spring 2006.
Charlotte, NC - probably WSOC in the 80's because of Headline News, but unsure on what year. WBTV did by the Fall of 1990 with All News Channel, then I think WCNC and maybe also WCCB a year later. (Also worth noting is that WCCB aired Home Shopping Spree every night except Sundays in Fall/Winter 1990).
Atlanta - would be either WXIA or WSB, sometime in the 80's.
Columbia, SC - WLTX? I saw a listing where they aired 80's sitcoms in the wee hours like Gimme A Break, Growing Pains, and Amen, preempting some of Up to the Minute/CBS News Nightwatch. This was in the early-mid 1990's.
Charleston, SC - WCIV? I have read they went 24/7 by 1991.
Florence/Myrtle Beach, SC - WBTW, which had all-night movies at least on Saturdays and Home Shopping Spree/CBS News around 1990-91. I'm guessing that's correct.
Greensboro/Winston-Salem/High Point (the Triad) - I've read WFMY was 24/7 in the 80's sometime after CBS News Nightwatch started in 1982. I think WXII followed by the early 90's.
WPVI was still signing off as late as December 1997. They would go off the air early Saturday and Sunday mornings around 4AM. By 1998, WPVI was 24/7.
In the Raleigh/Durham market, WFMY-TV in next-door Greensboro was the only thing on-air for 24 hours until the late 1980s when Goldsboro-licensed independent WYED-TV 17 signed on with lots of Home Shopping Network fare. I want to say the big stations in town went 24 hours in the early-to-mid 1990s.
By market:
In Greenville-Spartanburg-Asheville WYFF was definitely the first by around 1987 or 88 (possibly earlier than that, with airing CNN Headline News and NBC Overnight News in late-night/early-morning). I'm unsure of the exact year. No other stations were 24/7 after that until WSPA in the Summer of 1995, when they were burning off Golden Girls reruns late Friday nights and airing syndicated first-run shows late Saturday nights. Also, WLOS signed off every night until ABC World News Now premiered in early 1992. WHNS began 24/6 operations for good by Fall 1988 (still signing off every Sunday night around Midnight-1 a.m. well into almost the late 90's); they were the last to go complete 24/7 in Spring 2006.
Charlotte, NC - probably WSOC in the 80's because of Headline News, but unsure on what year. WBTV did by the Fall of 1990 with All News Channel, then I think WCNC and maybe also WCCB a year later.
Atlanta - would be either WXIA or WSB, sometime in the 80's.
Columbia, SC - WLTX? I saw a listing where they aired 80's sitcoms in the wee hours like Gimme A Break, Growing Pains, and Amen, preempting some of Up to the Minute/CBS News Nightwatch. This was in the early-mid 1990's.
Charleston, SC - WCIV? I have read they went 24/7 by 1991.
Florence/Myrtle Beach, SC - WBTW, which had all-night movies at least on Saturdays and Home Shopping Spree/CBS News around 1990-91. I'm guessing that's correct.
Greensboro/Winston-Salem/High Point (the Triad) - I've read WFMY was 24/7 in the 80's sometime after CBS News Nightwatch started in 1982. I think WXII followed by the early 90's.
WLOS did sign off every night, but it got pushed back on Fridays for In Concert '91(later named ABC In Concert in January 1992) or American Gladiators on early Saturdays/early Sundays. I've always wondered why WLOS signed off on weeknights rather than use a all night news feed.(like Headline News or even something else.)
WSPA's sign offs were sometimes pushed back, like during the 83 NCAA Tournament when there was a triple overtime game. Can't say for sure about WYFF or WLOS, but there must have been some delayed sign offs there too.