https://supreme.justia.com/cases/federal/us/71/333/
...9. The power of pardon conferred by the Constitution upon the President is unlimited except in cases of impeachment.
It extends to every offence known to the law, and may be exercised at any time after its commission, either before legal proceedings are taken or during their pendency, or after conviction and judgment.
The power is not subject to legislative control...
No, but judicial interpretation, yes.