I've seen this two-hour movie premiered on April 20th and in other places later in September of 1980.

Does anyone know the correct date?

Both IMDb and Wikipedia give the original US air date of 'Carnival of Thrills' as September 16, 1980 (with the former also listing a premiere date of February 21/28, 1981 in the UK and November 23/24, 1982 in Germany). They also agree that the next episode, 'Enos Strate to the Top', wasn't shown until November 5, 1980.

Both sources are publicly editable, so I won't call them definitive, but I did find the advert below in an article about the 1980 Fall Preview edition of TV Guide.

On 5/24/2019 at 11:02 PM, tripflicky said:

I've seen this two-hour movie premiered on April 20th and in other places later in September of 1980.

Does anyone know the correct date?

It's good to hear from you tripflicky. My DVD set say that Carnival of Thrills originally aired in the US on September 16, 1980. I have an old list from epguides (by Thomas D.L. Sisco) that agrees with that date. I wish my old TV guides weren't so buried or I'd pull them out. It was a season premier and they were always in September. We hope to hear more from you. 

Carnival of Thrills was one of my 5 or so that I don't like. It's the goofiest one of all. I don't like Bo and Luke fighting either.

Hey!

Thanks for having me & helping out here. 

So - problem is, September 16th, 1980 was a Tuesday.

According to this video, it was a Sunday two-hour movie. 

And since Guayana Tragedy was aired on CBS on April 15th, 1980 -  I'd say Sunday, April 20th is correct?

5 hours ago, tripflicky said:

 

 April 15th, 1980 

I turned 20 that day...7 days after John Schneider turned 20.  I hope we can get to the bottom of this Dukes mystery. I bet Boss and Rosco are behind all this....probably some scheme for Boss to make a few bucks.