Most people ask this the wrong way
If you are searching for this, you are doing a calculation in your head: I have a full-time job, so how much of my time will this take?
But most of the answers come from people who do this full time. They are describing a different life - sitting from the open to the close. That is not your situation.
Watching longer does not make you trade better. It only makes you trade more.
And the more you trade, the easier it is for your emotions to lead. The real answer is not in the hours. It is in which stretch you pick.