I think I contradicted myself in the post above, or at least wasn't very clear.
It depends if you're adding the adjustment to the movie time or subtitle time.
Imagine a subtitle at 0:30 again.
Subtitle time: Add +1 to the 0:30 subtitle time, so show at 0:31 movie time: Positive = Later
Movie time: Add +1 to the movie time when picking a subtitle, so when the movie is at 0:29, show the subtitle from 0:30: Positive = Sooner
I guess both approaches seem reasonable to me. I sometimes think about numbers weird, so am happy to follow popular opinion here.
Would changing the name from "Timing" to "Delay" clear anything up?