December 21st is always the shortest day of the year and the day at which it gets dark the earliest.
However after the December 21st day the days start getting longer by a minute each day.
Then when summer is here it stays daylight a lot longer.
You'll begin noticing the daylight staying longer after the 21st of December but it will only be a minute or so longer each day.
It becomes even more noticeable around January or February as the daylight stays out even longer.