chèn
趁热打铁
chèn rè dǎ tiě
Strike while the iron is hot.
趁风起帆
chèn fēng qǐ fān
Hoist the sail while the wind blows / Take advantage of favorable conditions.
趁天还没黑，快点儿赶路吧。
Chèn tiān hái méi hēi, kuài diǎnr gǎn lù ba.
While it's still not dark, let's hurry on our way.