～折(に)— On the Occasion Of

• 東京にいらっしゃった折には、ぜひお立ち寄りください。

  Tōkyō ni irasshatta ori ni wa, zehi otachiyori kudasai.

  When you come to Tokyo, please do stop by.

  いらっしゃった (honorific past) + 折には = a polite 'on the occasion when you come.'

• 先日お会いした折に、その話を伺いました。

  Senjitsu oai shita ori ni, sono hanashi o ukagaimashita.

  When I met you the other day, I heard about that matter.

  お会いした (humble past) + 折に refers politely to that specific occasion.

• 帰国の折には、お土産を買って帰ります。

  Kikoku no ori ni wa, omiyage o katte kaerimasu.

  On the occasion of returning home, I'll buy souvenirs to bring back.

  帰国の (Noun + の) + 折には marks the occasion of returning home.

• ・Register: polite/formal; frequent in letters and greetings.
• ・Often pairs with honorific/humble verbs.
• ・折 tends to refer to a good or notable opportunity, unlike neutral 時.
• ・折から / 折 also appears in set seasonal-greeting phrases (寒い折から).

Commonly confused with

The JLPT rarely asks whether you recognise a pattern — it asks which of several similar patterns fits. These are the ones ～折(に) is tested against.

• に際して — On the Occasion Of
• に先立って — Ahead of the Event
• につけ — At Every Turn
• ～にわたって — Spanning the Whole Range
• ～たび(に) — Every Single Time
• ～あげく(に) — After All That, In the End
• ～かと思うと／かと思ったら — No Sooner Than, Just When
• ～末(に)／の末(に) — After All Was Said and Done