AP Photo/Charles Dharapak

Congress officially delivered the bill to avert the fiscal cliff to the White House this afternoon, House Speaker John Boehner's office told ABC News.

Now the question is when will the President sign it?

The bill, passed late on New Year's Day, expires tomorrow at 11:59 a.m. when the current session of Congress concludes. If President Obama doesn't sign it by then, constitutionally the bill is dead.

But this evening, eighteen hours before the deadline, the President is on a golf course in Hawaii. And the bill is in Washington at the White House.

Administration officials won't say what they will do despite repeated inquiries from ABC News.

There seem to be two options: 1) An Air Force jet can deliver the bill to Hawaii (better leave quickly!) in time for the President to sign it before 11:59 Eastern Standard Time; or, 2) The White House can use a presidential "auto-pen."

The simple mechanical device uses a template of the presidential signature to scrawl it on paper if activated by the White House at Obama's direction.

But would an auto-pen - usually used to sign insignificant correspondence and photographs - pass constitutional muster? We don't know. The question has never been tested by the courts.

A 2005 legal study commissioned by former President George W. Bush determined that use of the autopen is constitutional but acknowledged the possibility that its use could be challenged. Bush never used the autopen, officials from his administration told ABC.

President Obama is only believed to have used the autopen once to sign a piece of major legislation - the 2011 extension of the Patriot Act - which reached his desk while he was on a diplomatic trip to Europe. Officials invoked national security concerns to justify the move.

Use of the autopen has been controversial. Conservative groups alleged last summer that Obama used an autopen to sign condolence letters to the families of Navy SEALs killed in a Chinook crash in Afghanistan - a charge the White House disputed flatly as false.

In 2004, then-Secretary of Defense Donald Rumsfeld was criticized for using an autopen to sign condolence letters to the families of fallen troops.

And in 1992 then-Vice President Dan Quayle even got into some hot water over his use of the autopen on official correspondence during an appearance on "This Week with David Brinkley." More HERE .

ABC News' Ann Compton and Devin Dwyer contributed reporting.