20%

So lets say your boss came up to you and said the following:

"Four days out of the week you work on what I tell you to work on.
On the 5th day you can work on whatever you want?"

Do you think this would have an impact on employees?
What would people work on?
Would they know what to do?
What would you work on?
Why aren't you doing this already?
Do you really need the bosses approval?

Think about it.