I’ve always treated it like this.
Put however many frames of black that you want at the head of your show….now step through the frames, and watch your waveform.
Black…black…black…black…first frame.
How do you know its the first frame?…because the waveform started to change.
In most broadcast outputs, im still putting slate and black before the first frame anyway, but the first frame is at 1 hour straight up, not 1 hour and 1 frame.
I’m sure someone will state otherwise, but I’ve never had a show sent back because it was 1 frame short.
Of course next you will be wondering about the end of the show…does it end on the last frame of picture, or the first frame if full black…assuming you do a fade out.