Assuming this program works like any other file recovery program, you will want to try to recover your file as soon as possible. Once windows thinks this is free space it could overwrite the area on the disk with new information, making your deleted file nearly unrecoverable. Because you have little to no controll over what part of the disk windows is going to use to write to next, a person can't really say when a file will become unrecoverable.
It's great to see such a useful program offered up for free. I plan to install this program on all of my client's machines once it is out of beta, and I have had a good chance to test it.