I have found what works for me on a delayed hatch is the water method for testing for movement.
Take a container that will hold enough water that the egg will have to float on it's own. Fill the contain with very warm water, not boiling but pretty warm tap water.
Ease the egg into the water and give the water a chance to settle down. Watch and see if after a few seconds, the egg will begin to bobble. Or not. If there is active movement, then by all means return the egg to the incubator and give it extra time.