〜までに

by (a deadline)

Gives a deadline: "by X". The action is done at some point before then.

Readings

How to form it

Put までに after a time: 金曜日(きんようび)までに (by Friday).
After a verb in the dictionary form, it means "before that happens": 暗(くら)くなるまでに帰(かえ)る (get home before dark).
The main verb is an action that gets completed, like 出(だ)す (hand in) or 帰(かえ)る (go home).

金曜日(きんようび)までに宿題(しゅくだい)を出(だ)してください。

Please hand in your homework by Friday.

十時(じゅうじ)までに帰(かえ)ります。

I'll be home by ten.

Using までに with an action that lasts. Say 三時(さんじ)まで待(ま)つ (wait until three), not 三時(さんじ)までに待(ま)つ.