split second 
noun
A very brief moment of time: for a split second, I hesitated...
- Harmless spirits will also occasionally pop up for split seconds, and snapping images of those also add to your score.
- I thought all this stuff in my head in a couple of split seconds, finally snapping out of my trance.
- Anastasius' eyes flashed for a split second and one dark eyebrow rose slightly.
adjective
Very rapid or accurate: split-second timing is crucial...
- His comic timing is polished up to split-second accuracy for the role of Elliot Richards, the hapless computer nerd that nobody wants to hang out with.
- During the hectic split-second timing of a campaign, this is a man who took time out to sit beside an old friend who was dying of cancer.
- It was a split-second decision to use force, he said.