The difference between the solar day and the sidereal day is caused solely by the progress of the earth in its orbit.
After 23 hours 56 minutes the earth has made a full rotation relative to the stars. But it has to turn for a further 4 minutes to get the sun to be above the same place on the earth.
The difference between the day lengths is one day divided the number of days in a year, i.e. approximately 24 hours / 365.
> Apart from these large-scale changes, over shorter periods weather and climate also have important impacts on Earth's rotation, causing variations in both directions. The fortnightly and monthly tidal cycles move mass around the planet, causing changes in the length of day by up to a millisecond in either direction.