助詞N4
〜までに
by... (deadline) / before...
Structure
時点 + までに
Explanation
〜までに marks the deadline by which an action must be completed, "by...". Unlike 〜まで (the action continues until that time), 〜までに means completion before that time.
Examples
レポートは来週の月曜日までに出してください。
Please submit the report by next Monday.
6時までに家に帰ります。
I'll be home by 6 o'clock.
Note
〜まで means the action lasts until that time (5時まで働く); 〜までに means completion by that time (5時までに終わる). Keep the difference in mind.