I've got a book about "Last of the summer wine", and it mentions the 1979 ITV strike. It does state that during the strike, the BBC did move some programmes to a more "prime" slot. In the case of LOTSW, it was moved from a 21:30 slot, to a 19:30 slot or 20:00 slot when a series was shown, during the ITV strike.
Well, it is a fact that Summer Wine really took off during the strike, it had run for a few series to middling ratings in a post-watershed slot, but the 1979 series was the most popular by far thanks to the strike. It also happened to be the first one shown before the watershed, although in the 40 Years of British Television book it does reprint a Radio Times letter from someone bemoaning "a once-favourite half hour of gentle humour has been turned into a situation comedy with canned laughter". Of course, it always had audience laughter.
The Guinness Book of Classic British TV says it got off to a slow start but the Beeb nurtured it by giving it slots vacated the previous week by other popular sitcoms like Reggie Perrin.
Although Summer Wine these days seems the ultimate Sunday teatime show, for the first few years it was a post-watershed show and it was pretty radical for the time, it probably felt a bit like The Royle Family did when it started because it was a bit of a departure from the standard sitcom. And its most popular series ever was in 1982 when it was on at 9.30 again.
I do know that Dez Skinn, the first editor of Doctor Who magazine, claims he got the magazine off the ground during the ITV strike because the Beeb did a documentary about comics during it which he was in and, because of the strike, everybody watched it. He says in one scene he was seen shouting at someone and came across as a big tough boss, so the next day when he had the meeting to discuss it, everyone was absolutely terrified of him and agreed to everything he said.