The Presidents' power of pardon is provided for in Article II, Section 2 of the US Constitution.
By appointing Article III federal judges to the Judicial Branch, and by granting pardons (may not grant a pardon for an impeachment).
The President is explicitly prohibited from pardoning someone who has been found guilty in an impeachment trial.
Sorry
Amnesty
Amnesty
The president has the power to give a pardon with the help of other officials. The president has the power to give a pardon with the help of other officials.
Many rights specifically granted to one branch of the US Government in the Constitution are thus prohibited to the other two. So any power specifically granted to the President or the Supreme Court (the Executive Veto for the first and the ability to find laws unconstitutional for the latter) are technically off-limits to the Congress. The Congress may also not pardon prisoners, as that is a right given to the President.
The president may use the pardon at any time for any federal prisoner. He can pardon anyone who has committed a crime against the United States, the only exception being that he can't pardon someone who has been impeached by Congress.
The US President can pardon any violation of federal law. He cannot use the pardon, however, to reverse a conviction that follows impeachment of an official. And he cannot extend a pardon to crimes that have not yet been committed.
No, the Senate cannot override a poresidential pardon.
There are no time limits set by statute for the granting of a pardon. If you have presented a petition to the Governor's Office requesting a pardon, then it can take as long as the Governor wishes to take in order to consider it.