This is entirely up to you really. For beginners, doing 30 minutes a day, five times a week is a great way to progress quickly. However with a busy modern lifestyle this may not always be possible. It really comes down to your personal motivations to learn the instrument. If you really want to play guitar, then you’ll make time to learn the techniques required, which is also one of the great things about online guitar lessons – you can take your lesson anytime, anywhere, no matter how busy your day has been.
If your aim is to go professional or become a session musician, then you’ll want to practice a lot more. Steve Vai allegedly practiced between 10 and 12 hours a day to achieve his impressive chops, but you don’t have to practice quite that much to get good. As a rough example, anywhere between 90 minutes right through to 4 hours has been cited as sufficient practice time by professional guitar players. The key is really in focusing your practice and making sure you’re always developing, rather than just noodling the same riffs for hours. Challenge yourself to learn new songs and techniques each time you practice and your progress will skyrocket.