I used Hal Higdon's novice training regime to train for about 4 months. The longest run is 20 miles. I never had cramping issues but suck did I have cramps starting at mile 18 during the race. I used a water bottle with a pinch of salt and pinch of sugar for training and the race. It worked really well for training but I wish I had experimented with sodium tablets which a lot of people do because of my race day experience.

Miles are more important than times. Especially early on. Don't skimp on the long runs.