strike while the iron is hot
Definition from Wiktionary, the free dictionary
- (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.
- (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.
Usage notes 
- When expressed in the imperative mood, this term is a well-known saying or proverb:
- Strike while the iron is hot!
act on an opportunity promptly
- Take advantage of opportunity.
- Gregory Y. Titelman, Random House Dictionary of Popular Proverbs and Sayings, 1996, ISBN 0-679-44554-4, p. 309.