It is not the time but speed. At 3000ft. you will be in G+Y as the RPM drops and also because you will get your speed to GD and below. But from FL350 where you would be attempting wind milling relight at 300kts you will have hydraulics. But as you drop the speed to GD for starter assisted or below for approach you will loose G+Y. Sully didn't need APU nor was he in G+Y loss or EMER ELEC because he had engines.