当口儿

chèn zhè dāng kou r

趁这当口儿

seize this moment

zhèng zài zhè guān jiàn dāng kou r tíng diàn le

正在这关键当口儿，停电了。

The power went out at this very moment.

shì qing fā shēng de dāng kou r

事情发生的当口儿

as it happened