Now, after 9 years I take more time on compositions and arrangements. Sometime I will spend 3-4 hours working on a peice of music and sometime I will play 30 min of scales, licks and improve solo.
I would say around 30 min to 1 hour daily for beginner would be enough. It's important not to push someone to play because you could really help him to quit. At first, guitar is hard and you need to practice chords, scales and a lot of finger exercises. It's not the most fun things to play and can get boring. 30 minutes of scales can feel like an eternity.