What is the minimum amount of sleep does a man require in a day? ?

7-9 hours for the average individual.
You can go to as low as 5 hours a night for up to 14 days without serious health issues. After this point you will begin to see physiological effects.

Read something I wrote earlier below about the subject.

In order for your brain to work at its optimal level you need 4 stages of REM sleep. REM sleep increase in duration with each cycle, for this reason just decreasing your sleep one hour can cut your total REM sleep in half for the night. For most people a cycle of REM and Non-REM sleep takes about 90 minutes. During REM sleep your brain absorbs the information it feels was important during the day and places it long term memory. What it feels was not important you forget. (Thatâ€™s why you never forget the hot girls name or phone number) LOL

Many Americans are chronically fatigued they rarely get 8 hours of sleep and when they do they feel ok, I am recharged. The truth is that it takes 27 days of 8 hours of sleep in a row for your brain to be at 100% It is impossible to judge your own impairment due to sleep loss because cognitive function is the first thing impaired with sleep loss. Also because many are always fatigued they think that it is normal. One trick to judge if you are fatigued is if you fall asleep within 10 minutes of going to bed you are fatigued.

You can also do things to let your brain know what is important and what is not. One trick is to take notes then read your notes into a recorder. Then either type your notes up or rewrite them neatly. Then listen to the recording a couple of times, you are basically telling your brain this is important store it in long term.

Many people also use alcohol in excess on a regular basic. Alcohol impairs the bodiesâ€™ ability to enter REM sleep. So even though you sleep long hours your body does not store information well and it has not cleaned your slate to absorb new information. Another bad habit is watching TV in your bed before sleeping. Your body gets used to a routine many people use TV as their routine before falling asleep. Even though they are exhausted they canâ€™t sleep with out watching TV. This is a bad habit there are only two things you should do in bed the first is sleep the other I will let you guess. But as a male the second is the best natural sleep aid I know of.