In my opinion, I prefer it when you follow the screenplay of the video. I mean, you don't need to fade the ending time of a sentence if it will finish when the video changes scene. I'll try to be clearer: the sentences ends at 1:00.00, and in that precise moment the video, in which there was a character since now, changes scene showing a landscape. You don't need to add a fading effect there, the video will "cut away" the sentence, and it will be pleasant to see (for me, at least). I think that fading effects aren't always necessary, if you follow the screenplay of the video. But, if in the future you need a little fading effect, consider that even a fade time of 100 can be perceived by human eyes. That may be useful for particle effects. I don't like seeing, for example, "dust effects" in which the dust vanishes without fading.
To answer your question: yes, \fad(250,0) works perfectly fine!