Lack of understanding of the relation between 24 hours and rotational period of Earth.

Earth does not take anywhere close to 24 hours to complete a rotation, regardless of how you measure it.

Earth rotates in 23h 56m 4s with relation to distant stars.

Earth rotates in 24h +- 30s with relation to Sun. The length of day depends on how far Earth is from the Sun, the speed at which Earth rotates the Sun changes throughout the orbit. And so every day the Sun makes a different distance around Earth (as seen from Earth), making the day a little bit longer or shorter.