[strike] while the iron [is] hot

to take action while the opportunity exists

The idiom "strike while the iron is hot" has its origins in blacksmithing, where iron is most malleable and easy to shape when it's heated to the right temperature. In a figurative sense, it means taking advantage of an opportunity or situation when the conditions are favorable or at their most advantageous.

He doesn't often make such offers - I'd strike while the iron is hot if I were you.
She decided to strike while the iron was hot and pitch her business idea to investors while interest in her industry was high.
The company chose to release their new product during the holiday season to strike while the iron was hot and capture a larger market share.
When the job offer came, he didn't hesitate and accepted it immediately, realizing it was essential to strike while the iron was hot.
In negotiations, it's crucial to strike while the iron is hot to secure the best deal possible.