届时
jièshí · HSK 7
at appointed time
⏰ 届时 = 届 (falls due) + 时 (time) = when the appointed time arrives
届 marks a due date or term coming round; 时 is time. Together they point to a future moment already set on the calendar, so 届时 means at that appointed time or on that occasion.
届 — corpse radical 尸 + 由
届 originally combined 尸 (a bent body) with a phonetic element, depicting someone arriving at a destination. Over time it came to mean 'to reach,' 'arrive at,' or 'fall due,' and is now used for sessions or terms (e.g., a graduating class) that arrive on schedule.
时 — sun 日 + temple/measure 寺
Originally a phono-semantic compound: 日 (sun) gives the meaning of time or season, while 寺 (shí) supplies the sound. Early forms used 之 as the phonetic before 寺 replaced it. The core sense 'season, time, hour' has stayed stable since ancient Chinese.