Please disregard what Reyes said.
edit: unless he is thinking you are transferring from the old still running tank to the new
Don't put fish in the tank 24 hrs after adding the water.
Unless you have a filter media that was still running in the old tank, then you can add the fish right away. If the media has dried out or been sitting without fish for a few days you'll need to cycle it all over again.
You don't want to do a fishy cycle if you can help it.
I was told the same thing, add water wait 24 hrs, and lost a lot of fish because of it.
If its brand new everything then follow the directions in this link.
http://www.aquariacentral.com/forums/showthread.php?t=64301
its a very well written explanation of what to do and expect.