@Walter Hinteler,
The President can pardon anyone he wants, anytime he wants.
You are correct, his power to pardon is absolute.
According to the story I linked to, the WH did not know about the money that was donated to the RNC by the father.
I think that Bush did the right thing when he rescinded the pardon.
It avoids the appearance of impropriety that would have occurred.
It also avoids the charge that the pardon was "bought" by the father.