One of my former teachers would tell you that no practice approach will produce results if done for less than 2 to 3 hours a day, yet practicing more than 5 or 6 would be a waste of time. Another one of my former teachers would say that amateurs will practice until they can play it right, while professionals will practice until they can't play it wrong. I would say this:
Even though this is a very popular question, unfortunately, it's a question that can only truly be answered by the person asking it.
We all look to teachers to help guide us, but they can only guide us based on their experiences. At some point each of us has to decide where we want to go.
In the case of practicing a guitar, the amount of time you practice daily will depend on a number of different factors like (a) what you want to play, (b) how well you want to play, (c) how much time do you want/have to dedicate to it.
The same materials are available to us all, but not all of us learn the same way. Not all of us want to play the same songs. Everyone is unique. So each of us must learn to steer our own ship based on our own ever changing desires, technical abilities and musical comprehension.
