届时 jièshí when the time comes
when the time comes; at the scheduled time
How to remember 届时: 届 measure word for events that come round each year + 时 time = when the time comes.
Characters
How it is used
- Formal connector meaning 'when that time comes / on the day' - 大会将于明日举行,届时敬请光临 (dàhuì jiāng yú míngrì jǔxíng, jièshí jìngqǐng guānglín) the conference is tomorrow; please attend when the time comes.
- Points back to a previously stated future time, typical in invitations, notices, and announcements. Written/official register.
- Spoken equivalent is 到时候 (dào shíhou); 届时 sounds much more formal. 届 here is the 'occasion' sense, not a period marker.