adverb
on the same day
Used to indicate that something happens or must be done within the same calendar day. Often appears in business or scheduling contexts.
See also: 今日中に (きょうじゅうに)
ご注文は同日中に発送いたします。
We will ship your order on the same day.
申請は同日中に処理されます。
The application will be processed on the same day.