General:
* Action speaks louder than words.
* Put your money where your mouth is.
* Time to get down to business.
* It's crunch time.
* The real work begins.
* Let's get started.
* Get to the point.
More specific, focused on implementation:
* Put into practice.
* Go into effect.
* Begin execution.
* Start the process.
* The ball is rolling.
Focusing on a challenge or test:
* Put to the test.
* Face reality.
* Prove yourself.
* Time to prove it.
* Walk the walk.
More informal:
* Let's do this!
* Time to put up or shut up.
* Show me what you got.
The best synonym depends on the specific situation and what you want to emphasize.