Once you have 0 in the display, the freezer should shut off right away, and there shouldn't be a delay. If the electronic control doesn't turn the freezer off when you set it to 0 off, you should ohm test the thermistor in a glass of ice water, waiting at least 5 minutes before testing, and it should read about 32.7K ohms. Unplug the freezer before ohm testing it! If the thermistor is okay, you'll likely need to replace the Electronic Control Assembly: searspartsdirect.com/product/z3nfu4jkjk-0046-253/id-297370602
It's very common for freezers to run a lot and depending on the location and ambient conditions it could run almost constantly. It's actually better for it run more and is more efficient. Starting is the hardest thing for a compressor and this is when most of the electricity is used. It's easier on the compressor and these units are very efficient.
If the freezer is running all the time, this may be due to hot outside temperature, the freezer being disconnected for a time so it is trying to cool down, freezer door not completely closing and sealing, worn or cracked gasket, or large amounts of food recently stored. Also, make sure the condenser coils are clean. Newer freezers have a smaller compressors, so may seem like they are running longer. This is better than them starting and stopping all the time. Try inserting a dollar bill in the door. Shut the door and see if the bill pulls out easily. If it does, the door is not sealing well and may need a new gasket. Try this at different areas around the door. Also place a thermometer between the packages in the freezer to check the temperature. If it is higher than 2-8 degrees, this is why it is running. If these possible causes check ok, then the problem may be with the temperature sensor or the sealed system. I recommend having a technician check if the problem is more serious than above. You can call Sears Home Services at 1-800-4-MY-HOME for repair.
You can find parts, diagrams, and your owner's manual here on Sears PartsDirect: searspartsdirect.com/model/3dfggysr6o-000582/kenmore-253280528012-upright-freezer-parts
If you need a refrigerator/freezer thermometer: searspartsdirect.com/product/5bknk0jlsd-0046-253/id-l304432837
If you need a Refrigerator Coil Cleaning Brush: searspartsdirect.com/product/5othfqw3jp-0046-106/id-4210463rw
Hope this helps!