ORN: 55 minutes, easy 4/2. I always start with a 5 minute warm-up walk, and finish with AT LEAST a 5 minute cool down.
Too many runners just walk out there door - or hop out of their car - and start running. Worse, they'll throw their leg up on something and pretend to stretch! OUCH!! Nothing good comes from stretching a cold muscle. But walking to warm up? It's a VERY good thing.
Many of the joint-type injuries that affect runners are simply caused by not giving all the joint-lubricating juices a chance to really get flowing. It's kinda like starting your car and then racing your engine before the oil has gotten warmed-up. You will do damage to your engine. You WILL do damge to your joints.
So, for me, 55 minutes breaks down to 5 minutes warm-up, 45 minute run/walk 4/2, 5 minute cool down. Try it. You'll like it. The investment in warming up and cooling down pays huge dividends.
Waddle on, friends.