This is a question that I get from a lot of beginner/intermediate players… and they always ask it with a mixture of excitation and apprehension in their eyes. The question is, of course: “How much should I practice guitar every day?”
The honest answer is: “It depends”
Firs of all, if you just started with guitar in the past 1-3 months, you should not practice too much or you may get injured. Your hands are just getting used to playing, and you do not want to risk stressing them too much 10-15m is ok, and if you really itch to do more then take 5m of rest before you start again.
Past this initial period, you still want to pay attention to your hands. So here’s a hard-and-fast rule that you cannot break, no matter what: NEVER practice in pain. If you feel any pain in your hands while you practice, you should stop and take a rest – no excuses.
But now let’s assume that your hands are fine (no pain) and that you are past the initial period of 3 months when your hands are getting used to play. How much should you practice then? In this situation, this still depends on what your goals are on the instrument.
If you want to become a professional, I would suggest you set apart 2h a day to work on your guitar. Mind you these are not two hours of pure technique! I would practice technique for one hour, and use the other one to work on other musical skills (improvisation, composition, repertoire, theory, etc…)
Note also that you can get good results in a shorter amount of time if you are really organized and focused in your practice. Personally, in the first few years I build the bulk of my technique by practicing 30m a day (I’m talking about pure technical practice) as that was the time I had. So do not despair if you do not have the time: get organized instead! Ask your teacher how to write and use a practice schedule… and follow it.
If you do NOT want to become a professional, but still want to enjoy playing, then anything from 15m to 1h can work depending on how busy you are in your life. And yes, you CAN get to a fairly high level of playing only with that kind of time: again what matters is being organized and focused.
A last important point: consistency matters. It’s MUCH better to practice 15m a day every day, than practicing 30m every other day, or 1h twice a week. If you have to miss a day every now and then that’s not critical, and if you want to take Sunday off that’s no problem either… but being as consistent as you can in your practice and trying to do something every day is what will take you far.
And in all that… do not forget to have fun with your guitar!