It depends on what you desire from your Parkour walk. Is this a Hobby? Or a serious discipline? Anyone who doesn't do a solid work out 3 days a week will probably get injured unless they've been working out consistently for a while or aren't trying to imporve their skills. If this a serious discipline for you, I suggest working out (including days where you just work on skills) 5-6 days a week. A good workout regimin is the APK Work Out of the Day E-mail & Crossfit style workouts in general.
Proper conditioning helps to avoid injury & increase skill level. Those who are really fit usually learn the Parkour Technique a lot faster then the "average" citizen

Hope that helps

P.S: Demon's Drills are also really good!!!