In the twinkling of an eye means immediately.
A twinkle in somebody's eye is a bright sparkle of light, especially when they are amused by something or feeling mischievous.
Twinkle (verb) – to shine with a flickering or sparkling effect.
Examples of use:
1. We saw a rare bird in the garden but in the twinkling of an eye, it was gone
2. They won £3000 but they spent it all in the twinkling of an eye.
3. Justine saw her train pull out of the station and in the twinkling of an eye, her day turned from good to bad.
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