at the appointed time; on the occasion

1. 由于我屆時已有約會／全部時間已經(jīng)排滿／另有事務性訪問，故不能出席。
   Because of a previous engagement/full schedule/business trip, I can't make it at the time.
2. 瑪麗將在最近某一天完婚，屆時你會在哪兒？
   Mary will get married one of these fine days, and then where will you be?
3. 由于我們屆時已有約會／全部活動已排滿／需要出差，故不能出席此次晚餐／午餐，實為抱歉。
   I/We regret that I/We can't make it because of a previous engagement/full schedule/business trip at that time.

時的英語翻譯：