I occasionally get asked this question a lot. Unfortunately, I don't know the answer. It depends on a lot of different factors such as how much you practice and what your goals are. For most guitarists I would definitley recommomed having two types of practice, the first being 'concentrated practice' and the other being 'practice for fun'. The former means the learner is logical and efficient at listening, playing and reading while absorbing all of the information they are learning. The latter, 'Practising for fun' could be playing music, improvising or listening. Basically anything that doesn't require too much brain activity and your not worried about how much time your putting into it.
When it comes to, let's face it, 'the boring stuff' of learning and memorising things like scales and technical pieces I will dedicate some time for concentrated practice. I often use a digital timer to limit my time spent on a scale or a few bars of music. I find that if I practice a scale for 2 minutes, everyday for a week, It will stick into my long-term memory much better. How many times have you tried to cram in a scale or some other information into your brain the day before a performace or exam? I know I have. That's why I try and stick to short practice sessions, but do them more often rather than one long practice session once a week.
I love picking up the gutiar from the stand and playing anything that comes to mind. A favourite riff or chord prgression, or even putting a backing track on and improvising. I might not progress as much as I should but it might just stumble on a new lick or chord voicing. Playing for fun is good for the soul, as most days I spend my time teaching with a guitar in my hands and often I don't want to play in my spare time.
So, set yourself a goal that is achievable within a reasonable amount of time (less than a year) and try set time for both types of practice. Try practising for less time but do it more often. It's always good not to think of practice as a chore, mix up concentrated practice and praticing for fun.
I'm not a big fan of the term, 'practice makes perfect' as practicing something with the wrong technique will only make you better at playing with the wrong technique. I usually say, 'Perfect practice makes perfect' as I try to explain an efficient way of learning.