As a mad scientist an eccentric and obsessive type, Cyrus is used to working through the night without stop. No matter how enthusiastic of an assistant Else is, you can't expect a little girl to keep up with that after her bed-time.
You also can't expect a father like him to keep working when his little pumpkin is practically falling out of her chair. The deepest secrets of science will still be there to unlock tomorrow - this is a school night!