This was a power that would take millennia to understand.

Processes that normally took millennia would occur in a single day or less.

The succession from open water to climax woodland takes centuries or millennia.

This accumulated knowledge must have taken several millennia to compile.

"Or it could take millennia," the chief engineer re-minded him.

Two hours had passed within the ship, but the light from the stars they had left behind would take millennia to catch up with them.

We all realized that it would take millennia to restore Earth and make it a place worth living.

The star system is too distant to see from earth and it would take millennia to travel there.

And we knew our world would take millennia to recover.

You can accomplish in a generation what took millennia on Earth.