This is my 3rd time doing C25K. First time did the whole thing on a treadmill which doesn't translate to running outside so it didn't go anywhere once I'd finished. Second time I did it outside and kept going and eventually got up to doing 3-5 mile runs, long runs of 10 miles and even a half marathon. A bum knee due to a fall on the ice put a stop to that. It's been several years, but I am starting again...just did week 2, day 2 this morning.
Taking the day off is pretty important, especially if you're starting as someone who wasn't running at all at the beginning. Trying to do too much too fast is a good way to end up with shin splints. I did my 2nd stint while I was overseas in Afghanistan so I was able to get regular runs in every morning. I was able to fast track things a little bit because I, literally, did one rest day between runs rather than say Mon, Wed, Fri.
Something that I did do that I would recommend is getting out and walking for 30 minutes on the off days. Any extra exercise is always good and that way I was able to stay on a regular routine.