Unfortunately Samsung Health does not automatically detect when you went to sleep or does it tell you how good you slept. For what you are saying, you would need to just to record the time you slept. You could try an app called sleepandroid. It's very useful.
if you have a Samsung smart watch it records automatically.. if not then I don't believe you can put it two different sleep times. they may have changed that as it's been awhile since I've manually entered sleep data as I've had a Samsung watch