Heidi, I bought my treadmill last February (about a year ago) and I was running 25 minutes straight until hmmm maybe August? I very slowly have increased. My treadmill came with a slot where you can put little chips in it that have workout programs set in and it changes every minute. So, once I completed the beginners 8 week training I just started changing the treadmill every minute on my own. Increasing as the weeks went by. So, don't beat yourself up if you can't do it in 3 or 4 weeks.
I think I've changed my mind, I don't feel like shopping in a rush today, even though I want something new this weekend and I'm never going to have to time to go.
I think I'll work through lunch instead.