Pittsburgh had lots of factors in the 50's which would have this make sense for WDTV.
- Lots of steelworkers on a three-shift schedule. It was pretty much a 24 hour town in those days
(as those of us who can remember bars that were packed full at 6AM can attest)
- WDTV had pretty much a monopoly in the #6 market in the country. There was ample
opportunity to time shift kinescoped shows that did not make the prime time schedule.
I believe you are correct that KDKA continued this after taking over the station, at least for some time.
I also remember WSTV in Steubenville, Ohio running "Movies Till Dawn" for many years. I think
they began doing it in the 60's.