。
The train departed at exactly 5:00.
Literal
Train [topic-は] 5-o'clock exactly [at-に] departed.
五時ちょうど ('exactly 5 o'clock') uses ちょうど ('just, exactly, precisely') as a post-nominal adverbial — attaches directly to the time expression to emphasize exactness. The synonym きっかり has a slightly crisper, more precise feel and is often used for round-figure exact times.