Doubtless continuity goofs are a thing. But have you tried considering that a movie is a narrative? Try imagining that there are actual real events that the storyteller is describing, and then imagine that storyteller is only human and considerably less attentive to minutiae than you are. Perhaps the storyteller forgets to tell about the time the cowboy switched revolvers, or spends more time talking about what the hero is doing than the remaining time on the fuse would seem to permit.