the last time you bogged this topic i might have said it depends on your age, your health and your work habits. You said you work nights and when you come home you see the sun coming up and that throws you off from being able to get a good night sleep.

when we are young we need more sleep as we get older we need less sleep and when we get really old we might need more sleep. If you are perfectly healthy and you get 5 hrs of sleep every day you should be ok. One in a while it helps to get 8 hrs of sleep because some researchers say that unless you experience REM sleep your not getting enough sleep. REM sleep is a period of time when we dream. whether we remember the dreams or not isn't important. but getting REM sleep is.

http://www.southend.wayne.edu/modules/news/article.php?storyid=945

good article on bbc.com on sleep deprivation.