expression, adverb
quickly; as soon as possible; without delay
Adverbial phrase emphasizing promptness; often used in requests or suggestions to do something early or right away.
早いこと返事をください。
Please reply as soon as possible.
早いこと始めたほうがいいよ。
You'd better start right away.
早く is the standard adverb form of 早い and is more common in everyday speech. 早いこと is a more emphatic or colloquial phrase meaning 'quickly' or 'without delay'.
Phrase composed of the adjective 早い (early, fast) and the nominalizer こと, literally 'early thing', used adverbially to mean 'quickly'.