An Instant
Instant, Moment
noun
A blink interval of time is a very short period of time. It's an instant or a moment.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
蜘蛛の巣にぶつかった瞬間に、人は突然空手の達人へと変身する。
The moment they walk into a spider web, people suddenly turn into karate experts.