Chèn rè (hǎo) dǎtiě.

趁熱(好)打鐵。

Lit While [it's] hot, (it's easier to) beat iron [into shape].

Fig (It's easier to) strike while the iron is hot.

Note [Compare chèn huǒ rè and dānglìng guǒzi below; chènrè-dǎtiě is used as a chengyu; see also the following entry.]

Topics chengyu chènrè-dǎtiě OPPORTUNITY TIMELESSNESS