How many repeats of that interval lunge? Are you meaning to do the full 5k as intervals?
(Not lunge, but…) At a guess for the 1′ on / 45″ off workout you’d probably repeat 8-10 times. This is just an example of an interval workout, and I’m sure lunge won’t contradict me when I say that other plans are available and also benficial 🙂
Just as an example, the last workout I did (last week) with my triathlon club we did 6x1000m intervals, first two at race pace, second two 10% faster, then last two at race pace again. 1 minute recovery between intervals. Most of us are half-ironman distance competitors (ie a half marathon run), so the longer intervals aren’t a problem, but if you’re building up to your first 10K this is probably too far!
Whatever distance you do make sure you’re fully warmed up beforehand – we usually do a 3km run and then some drills before starting. You should also include another 2k or so to cool down after.