(spoiler alert) I remember the countdown scene in the GalaxyQuest, “It always stops at one.”
A nick-in-time can be nuanced too, especially when both parties are responding to the other’s presence. (ie, villain accelerates the schedule of his attack because he sees the heroic forces moving in, and the heroic forces punch on the gas.) Is it a deus ex or not?
And sometimes, one can get so involved in writing the story that it’s easy to miss the fact that a deus ex is forming, due to desire that the story resolves itself favourably for the main characters. In my potter fanfics, once I became aware that I was doing it, I cut back, and either: 1) let some situations turn out negative (which happens), or 2) rewrite to avoid the particular situation, perhaps with a different scene that turns out similar w/o the deus ex. And now that I’m writing originals that I want a good deal of realism too, I generally avoid them.