Control is more important than speed. Slow at first is always best, only play as fast as your ability to maintain control. Goes pretty much for any instrument really, not just guitar. Also, don't push yourself to complete two hours worth of learning in two hours. Six sessions of twenty minutes over a longer period of time is likely to be far more productive because it allows you time to absorb the learning to a much greater depth and that means you'll be less likely to forget it.