Watch the Organizing Practice Sessions online guitar lesson by Bruce Arnold from Jazz Guitar for Beginners
Each student is different so the amount of time you have to practice will vary. First off, remember that you need to build up to your maximum practice time over a few weeks or months.
Get in the habit of adding a few minutes each day and over time you will find you are used to practicing longer periods without getting fatigued. Do mental practicing.
Imagine the fretboard in your mind and mentally run over all the scales, arpeggios and chords that you have learned. This will greatly help in memorizing all the information.