I did it!
At 8pm yesterday, I got my sneakers on and went out for awalk. I didn't bring my watch (it was in the bathroom and I only realized after I had tied my sneakers and as I had vacuumed earlier in the day I didn't want to tiptoe in to get it) but decided to be out for at least 8 songs from my mp3-player. Figured that would be at least 30 minutes.
Coming back home I found out I had been out walking for 45 minutes. Felt good! :)