27th day of the month
27 days
「二七日」 has another reading with different meanings.
二十七日に届いた通知を確認した。
I checked the notice that arrived on the 27th.
会議は二十七日に変更になった。
The meeting was changed to the 27th.
今月の二十七日が提出期限だ。
The submission deadline is the 27th of this month.