までに— By / No later than (deadline)

• 5時までに帰ってください。

  Goji made ni kaette kudasai.

  Please come home by 5 o'clock.

  5時までに = by 5 o'clock (deadline)

• 夏休みが終わるまでに宿題を全部やった。

  Natsuyasumi ga owaru made ni shukudai wo zenbu yatta.

  I finished all my homework before summer break ended.

  終わるまでに = by the time it ends (before that endpoint)

• 明日の朝までにレポートを提出してください。

  Ashita no asa made ni repooto wo teishutsu shite kudasai.

  Please submit the report by tomorrow morning.

  明日の朝までに = by tomorrow morning (deadline)

• ・までに (deadline: by X) vs まで (continuation: until X): 6時まで働く (work UNTIL 6) vs 6時までに仕事を終わらせる (finish work BY 6).
• ・までに → the action must be completed before the time point.
• ・まで → the action continues up to the time point.

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones までに is tested against.

• 間 (あいだ) — Throughout a Duration
• 間に (あいだに) — A Point Within a Window
• あとで — After (with a time gap)
• 頃 / ごろ — Around / About (approximate time)
• 〜おきに — The Gap Logic (Intervals)
• たばかり — Just did (subjective recency)
• たところ — Just finished (this very moment)
• ているところ — In the Middle of Doing