NHS Couch to 5k - Day 1.

I have down loaded a podcast of the NHS C25K it is a nine week program to help me get from a couch potato to running 5km without dying. Because of the weather I am only running on the treadmill at the gym at the moment, cold weather not good for the old asthma don't ya know.
I can't believe its been four days since my last workout, time flies don't it?
After a 5 min walk at 5kph to warm up I alternated 60 sec's of jogging and 90 sec's of walking then a 5 min cool down to finish.

Time 30 mins
Dist 2.7 km
AvSp 5 kph
AvHr 125 Bpm

I felt that I could/should do more than that so I carried on until...

Time 52 mins
Cals 320
Dist 4.2 km
AvSp 5 kph
AvHr  120 Bpm

At the end of the pod cast it said to have a rest day between work outs, anyone know why that is?