There are a few variables that affect how long the freezer will run. Most automatic defrost styles run a lot. This is not necessarily a sign of a problem.
Today's units have smaller compressors which are more energy efficient than units in the past. They run more but they use less electricity.
If your freezer is empty this could be normal. With no food in the freezer it takes a long time to cool the box down and it will warm quicker without food.
Put some plastic containers of water inside the freezer and fill it around 1/2 full. I think you will see a big difference.
You can also try turning the thermostat to a warmer setting. If it is on maximum when you turn it back at some point the freezer should cut off. If it doesn't it might indicate a problem with the thermostat. Give any temperature changes 24 hours to take effect.
As long as the temperatures are being maintained most likely the freezer is working normally.
I hope this information is helpful to you but submit another question with any additional details for further assistance.