1.
as soon as possible; without a moment's delay; at the earliest possible moment
An emphatic expression conveying extreme urgency, meaning not even a single moment should be wasted. Stronger and more literary than できるだけ早く.
Usage
一刻 literally means "one moment" or "one instant." The expression 一刻も早く conveys that even the smallest unit of time matters — there must be no delay. It is more emphatic and literary than できるだけ早く or なるべく早く. Often used in urgent situations involving safety, emergencies, or critical deadlines.