An estimate is an estimate, not a quote. If the estimate is to get it done by Tuesday, and is turned out it will take 2 times longer, do you just work 16 hours

An estimate is an estimate, not a quote. If the estimate is to get it done by Tuesday, and is turned out it will take 2 times longer, do you just work 16 hours a day or pay a second programmer to help to get it done by Tuesday?