Strike-while-the-iron-is-hot Definition

verb

(literally metallurgy) To strike a hot piece of metal, especially iron, with a mallet or other tool before it cools, while it is still hot enough to be shaped.

Wiktionary

(idiomatic) To act on an opportunity promptly while favorable conditions exist; to avoid waiting.

We should strike while the iron is hot and order some immediately, before they change the offer.
Wiktionary