at a moment's/minute's notice
or US on a moment's/minute's notice or at short notice or US on short notice
: immediately after you have been told about something一经通知立即 -
They're prepared to help us at/on a moment's notice. [=as soon as we tell them that we need their help]他们准备好一有通知就来帮我们。
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They can be ready to go at/on a moment's notice.他们可以随时准备出发。
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She had to leave on a business trip at/on (very) short notice.她一有通知就必须出差。